Interactive computerized modules have been linked to improved retention of material in clinical medicine. This study examined the effects of a new series of interactive learning modules for preclinical medical education, specifically in the areas of quiz performance, perceived difficulty of concepts, study time, and perceived stress level. We randomly allocated 102 medical student volunteers into control and experimental groups. All participants studied selected anatomical and physiologic concepts using existing material (lecture notes, textbooks, etc.), while those in the experimental groups used the new interactive modules as well. All participants completed a quiz to test their knowledge of the assigned concepts and a survey to assess their subjective experiences in studying with the modules. We found a trend toward higher quiz scores in the experimental group relative to the control group, though it did not reach statistical significance (P = 0.31). Perceived concept difficulty was significantly reduced among those who studied with the modules (P less than 0.001), and the number of hours spent studying the concepts was significantly increased (P = 0.028). Of those who used the modules, 83% rated them as "very helpful" or "extremely helpful." No significant differences existed between participants' reported stress levels during the course of the study (P = 0.44). Our data suggest that medical students may learn more effectively and feel less intimidated by difficult concepts when interactive modules supplement traditional instruction. (Contains 1 table and 2 figures.)