Active sniffing in rodents at theta frequency during exploratory behavior has been hypothesized to enhance odorant access to the receptor sheet and to evoke activity patterns in olfactory and limbic structures which facilitate induction of synaptic plasticity. The present results demonstrate a third potential consequence of theta frequency sniffing -- reversible enhancement of lateral/feedback inhibition in the rat olfactory bulb. Suppression of mitral/tufted cell single-unit spontaneous activity evoked by single lateral olfactory tract (LOT) shocks was examined during LOT stimulation at either 1 or 5 Hz (theta frequency). Theta frequency stimulation rapidly and reversibly enhanced LOT-evoked suppression compared with 1 Hz stimulation. This enhancement was not stimulus intensity dependent. Sniffing-induced modification of lateral/feedback inhibition may enhance odor processing during exploration.