This opinion involves two separate appeals, arising from the joint trial of the instant appellants. The facts are identical and the appeals raise the same issue. We therefore address ourselves to both appeals herein.
On August 10, 1974, Catherine Chavis was upstairs in her home at 528 Fallon Street in Philadelphia, when she heard a voice calling from below. She came out of a room and saw two men proceeding up the stairs. The first man, later identified as appellant William Green, was carrying a sawed-off shotgun. Ms. Chavis turned, ran into her bedroom and locked the door. She then climbed out the bedroom window and dropped onto the *141roof below. While on the roof, she heard her bedroom door being forced open. She entered her neighbor’s house through a bedroom window and went downstairs and outside, where she was met by the police.
Three Philadelphia policemen accompanied Ms. Chavis back into her house where two guns, her pocketbook, and certain records were found to be missing from the bedroom. Ms. Chavis knew both of the intruders as being from the neighborhood. She went with the police to Green’s house, approximately a block and a half away at 4930 Hoopes Street. Both appellants were found there, identified by Ms. Chavis, and arrested. Subsequently, the police obtained a warrant and made a thorough search, lasting approximately an hour and a half, of Green’s residence. Mrs. Green, appellant Green’s mother, was in the house when the police arrived and remained there throughout the search. The search did not reveal any of the missing items from Ms. Chavis’ home but the police did find used hypodermic needles and a package containing at least 1,000 glassine bags.
The appellants were jointly tried before a judge, sitting without a jury. Both were found guilty of robbery,1 criminal conspiracy,2 unlawfully carrying a firearm without a license,3 possessing instruments of crime4 and burglary.5
The sole question presented in this appeal is whether the court below erred in refusing to declare a mistrial when the prosecuting attorney introduced the topic of certain drug-related paraphernalia which was discovered during the police search of the premises *142where the appellants were found. This matter was first broached during the testimony of Mrs. Green, who was an alibi witness for the appellants. She stated that both Green and Williamson had been at her house during the time of the robbery. The following exchange took place during the cross-examination of Mrs. Green by the prosecuting attorney:
Q. Did you go with the officers when they searched your house; did you go throughout the house with them?
A. Yes.
Q. Did you see them search the rafters ?
A. Yes, they took a mirror. I gave them a mirror. They took a big flashlight like' this, and you have got to put it underneath the panel, and they could look up like this, that they turned over my trash.
Q. What did they find in the rafters ?
A. Nothing, nothing but a baseball bat.
Q. They didn’t find nothing?
A. No, no guns, no nothing.
Q. Are you sure they didn’t find a large amount of glassine bags?
MR. MONTGOMERY: Objection.
THE COURT: Overruled.
THE WITNESS: No, I don’t think so.
BY MR. CARPENTER:
Q. Are you sure they didn’t find any hypodermic . needles?
MR. MONTGOMERY: Objection.
THE COURT: Overruled.
THE WITNESS: I don’t think so because they didn’t. I would have said something about it.
BY MR. CARPENTER:
Q. But you were there?
*143A. Yes, but it was more than one officer. I had about 20, and I couldn’t watch everyone.6
In rebuttal, a police officer present at the search testified for the Commonwealth. The prosecuting attorney conducted the following examination.
BY MR. CARPENTER:
Q. Did you participate in the search of the premises? A. That’s correct.
Q. Did you search the rafters in the basement?
A. Yes, sir, I participated in that part of the search. Q. And what if anything had you recovered from there?
MR. HANFORD: Objection.
THE COURT: Overruled.
THE WITNESS: In the course of the search of the rafters, we found a couple of used hypodermic needles and a package, more like a cardboard container containing at least 1,000 glassine bags—
After this testimony by the police officer, counsel for the appellants joined in a motion for a mistrial, which was denied. We hold that the lower court’s refusal to declare a mistrial was proper and we affirm the judgment of sentence entered below.
The appellants’ assertion that a mistrial should have been granted, based on the testimony regarding the hypodermic needles and glassine envelopes found on the searched premises, rests on two separate arguments. *144First, it is alleged that the Commonwealth’s evidence on this topic did not, in fact, rebut the testimony of the defendant’s alibi witness, Mrs. Green. Citing the well-established proposition that a witness cannot be impeached on a collateral matter, appellants insist that this testimony was improperly admitted. The appellants’ second argument is that the introduction of drug-related evidence in a prosecution for a separate offense is, regardless of relevance, so overwhelmingly prejudicial as to require a mistrial or, in this case, reversal of a conviction.
The frame of analysis applicable to the instant case is suggested in Commonwealth v. Quarles, 230 Pa.Super. 231, 326 A.2d 640 (1974). Referring to evidence of drug addiction introduced in a trial for robbery, this court stated that “before the [trial] court permits such testimony over objection, it should consider the inherently prejudicial nature of such testimony and carefully determine whether its probative value and need is sufficiently strong to justify its admission.” 230 Pa.Super. at 235-36, 326 A.2d at 642.
We must, therefore, weigh the probative value of the disputed testimony against the possibility of prejudice to the appellants. Mrs. Green was an alibi witness, testifying that the appellants were at her house at the time when the robbery occurred. Her credibility was thus a matter of major importance at trial. The accuracy of the witness’ observations, her awareness of the particular events which transpired in her house that day and her ability to recall such events were all relevant. If the witness was incorrect in her stated conclusion that the police found nothing in the rafters but a baseball bat, the finder of fact might also infer that she had been wrong in her belief that the appellants had been in the house at the time of the robbery. Mrs. Green testified that she was present when the rafters were searched and that nothing was found but a baseball bat. The particularity *145of her testimony on this matter was not impaired by her later caveat that she “couldn’t watch everyone.”
Further, if the fact finder chose to believe that Mrs. Green lied when she denied knowledge of the attested results of the search, the possibility that she might lie to provide an alibi for her son and his friend would be apparent and could, at the very least, affect the weight accorded to her testimony. Considering these factors, we find the challenged testimony to be clearly relevant.
Appellants attempt to draw an analogy between the instant facts and the fundamental common law principle that evidence of a defendant’s prior criminal activity cannot be introduced as substantive evidence of guilt of the present charge. This reasoning is inapplicable, however, as this court has specifically rejected “the argument that a reference to the drug addiction of the accused necessarily carries with it the inference that the accused has engaged in prior criminal conduct. Commonwealth v. Quarles, 230 Pa.Super. 231, 326 A.2d 640 (1974).” Commonwealth v. Williams, 230 Pa.Super. 72, 75, 327 A.2d 367, 368 (1974). No evidence as to the use or sale of narcotics by either of the appellants, other than the disputed testimony, was introduced at trial. Under these circumstances, especially in a nonjury trial, we cannot equate such testimony, offered for a legitimate purpose, with evidence of prior criminal conduct.
Concluding that the questioned testimony was relevant and was not so prejudicial as to require reversal per se, we must determine what prejudice, in fact, inured to these appellants. Here the trial judge, in his supporting opinion, states that “such evidence was not of such prejudicial nature as to influence the Court’s decision as to the guilt or innocence of the defendant.” We perceive no reason, on' the record before us, to doubt this conclusion.7
*146Our final inquiry, the result of which is somewhat foreshadowed by the preceding discussion, is whether the trial court abused its discretion in refusing the motion for mistrial. “The decision whether to grant a mistrial on the ground of prejudicial testimony is initially within the sound discretion of the trial court.” Commonwealth v. Koch, 446 Pa. 469, 477, 288 A.2d 791, 795 (1972). It has often been held that, to require a mistrial, the situation must be such as to raise a fixed bias in the mind of the fact finder and thus to preclude a fair and objective verdict. See Commonwealth v. Carlos, 462 Pa. 262, 341 A.2d 71 (1975); Commonwealth v. McNeal, 456 Pa. 394, 319 A.2d 669 (1974). The trial court found that the testimony involved herein did not create such prejudice or otherwise influence its verdict.
The judgment of sentence of the lower court is affirmed.
SPAETH, J., files a concurring opinion.
HOFFMAN, J., files a dissenting opinion in which JACOBS, J., joins.