To investigate whether motor skill learning depends on de novo protein synthesis, adult rats were trained in an acrobatic locomotor task (accelerating rotarod) for 7 d. Animals were systemically injected with cycloheximide (CHX, 0.5 mg/kg, i.p.) 1 h before sessions 1 and 2 or sessions 2 and 3. Control rats received vehicle injections before sessions 1, 2, and 3. Although CHX did not affect improvement of performance within session 1, between-session improvement was impaired. In overtrained animals, comparable injections of CHX had no effect on rotarod performance. These findings suggest that consolidation of motor skills requires protein synthesis. (Contains 2 figures.)