We studied effects of selective blockade of N-methyl-D-aspartate (NMDA) receptors in the primary somatosensory cortex (SI) of the adult cat on reorganization of cortical maps after selective deafferentation. About two weeks after hindlimb deafferentation, cortical loci representing the 'trunk' seemingly expanded and 'migrated' into areas originally devoted to the 'hindlimb'. Selective blockade of NMDA receptors of the SI cells by continuous infusion of 2-amino-5-phosphonovalerate (APV) into the cortex disrupted such change. The APV treatment also depressed responses of SI cells to natural sensory stimulation, but left no long-lasting side effects. The results suggest that the processes of map reorganization take place within the SI and involve mechanisms dependent on NMDA-receptor-mediated activity.