Early unilateral olfactory deprivation produces large structural and neurochemical changes in the olfactory bulb, the first central relay for olfactory information. The functioning of deprived bulbs was examined in the present report by using paired-pulse stimulation of the lateral olfactory tract. Paired-pulse stimulation reflects interactions between mitral/tufted cells and granule cells, as well as the modulatory effects of centrifugal and intra-bulbar association fibers. Paired-pulse stimulation produced inhibition of mitral/tufted cells in control animals at PN20-PN22. This inhibition was significantly enhanced in littermates deprived of olfactory input from PN1 to PN20-PN22. Suppression of mitral/tufted cell single-unit spontaneous activity following single-pulse stimulation of the lateral olfactory tract (LOT) was similarly enhanced in deprived bulbs. These results suggest that early olfactory deprivation significantly modifies subsequent olfactory system function.