Abstract This study reports changes in the protein pattern and incorporation of l-[U- 14C]-leucine in brain cells of the hippocampus and sensorimotor cortex of rats. The following subcellular fractions were analyzed by SDS-acrylamide gel electrophoresis: plasma membranes, synaptosomal membranes and synaptic mitochondria. Recurring reversal training gave an increased synthesis of synaptosomal membrane proteins with mol. wt. 35,000–45,000 and 60,000 and 100,000 in trained animals compared to active controls. Lesser changes were observed in plasma membrane and synaptic mitochondria fractions. Of the brain areas studied, the hippocampal synaptosomal fraction showed an initial, temporary response, and the cortical cell fractions responded subsequently. Judged from the time sequence of the protein response, it seems that recurrent reversal training induces a change in synaptic protein towards higher molecular weights, suggesting that these changes reflect a modification of the distribution of synaptic protein.