The purpose of this study was to examine the effects of interleaving and expanding retrieval on the retention of physiology concepts. Participants (n = 189) read and then reread 30 immunology and reproductive physiology passages. Half of the participants read and then reread the passages in a blocked manner (e.g., a1a2a3b1b2b3), and the other half did so in an interleaved manner (e.g.,a1b1b2a2a3b3). Participants were then repeatedly assessed, without feedback, after either a uniform or an expanding series of intervals. Half of the students from both the blocked and interleaved groups completed the assessments 1, 2, and 3 days after rereading the passages (uniform), whereas the other half completed the assessments immediately and 1 and 3 days after rereading the passages (expanding). All participants completed a final assessment 10 days after rereading the passages. There were no significant differences between the blocked and interleaved groups on any of the assessments, nor were there any significant interactions between the groups on any of the assessments. Those in the expanding retrieval group scored significantly higher than those in the uniform group on all four assessments (ANOVA; assessment 1: F = 35.12,P = 0.00; assessment 2: F = 13.88, P = 0.00; assessment 3: F = 10.87, P = 0.00; and assessment 4: F = 6.79, P = 0.01). Mean final assessment scores were 47.58 ± 19.81 and 40.50 ± 17.17 for the expanding and uniform groups, respectively. The results indicate that participants benefited more from expanding retrieval practice.