This research was occasioned by prevalent criticism that under the current civil jury system, jurors cannot adequately evaluate complex expert testimony. Participants (n=54), who served as mock jurors, watched a videotaped trial in which two scientists provided evidence on whether polychlorinated biphenyls (PCB's) could have caused a plaintiff's illness. The complexity of the expert's testimony and the strength of the expert's credentials were varied in a 2 x 2 factorial design. After watching the videotape, mock jurors rendered a verdict and completed a number of attitude measures related to the trial. Consistent with the study hypothesis, findings show that jurors were more persuaded by a highly expert witness than by a less expert witness, but only when the testimony was highly complex. When the testimony was less complex, jurors relied primarily on the content of that testimony, and witness credentials had little impact on the persuasiveness of the message. 25 references