The acquisition of skilled motor performance is characterized by a distinct time-course indicating a multistage process of learning (Karni et al 1998; Hikosaka et al. 1999). We have recently shown that within 24 hours post-training, robust quantitative and qualitative changes occur in the knowledge of a trained sequence of movements, in a step-wise manner (Korman et al SFN 2001). Here, we present behavioral data supporting the conjecture that human motor learning is subserved by a process similar to that subserving the consolidation of perceptual skills (Karni et al. 1994; Stickgold et al. 2000). To test the relative contributions of time versus time in sleep to delayed gains in motor performance we measured the speed and accuracy of sequential finger tapping movements using the non-dominant hand in 15 right-handed individuals at two sessions spaced 12 hours apart. An over-day (OD) group was tested and trained in the morning and re-tested in the evening with no sleep allowed during the day, whereas the par...