We investigated the influence of a retention interval spent sleeping or waking on participants' performance in spatial, auditory, and visual tasks. Using Jenkins and Dallenbach's research (1924) as a paradigm, we replicated and extended the original study using a 2 X 3 mixed design with repeated measures. The 2 independent variables were the activity during the retention interval (i.e., sleeping or waking) and the 3 types of memory tasks (i.e., spatial, auditory, and visual). Fifty-seven undergraduate students participated in 2 sessions. Results indicate that a retention interval spent sleeping had a beneficial effect on auditory memory performance. We did not find a significant effect for visual and spatial memory performance, but attribute this to ceiling effects within the experimental design.