The present studies began an examination of the process by which unilateral odor deprivation results in a 25% reduction in the size of the olfactory bulb. Rat pups had a single naris occluded on the day after the day of birth (Day 1) and were tested at several early postnatal ages. Dopamine (DA) levels were measured to gauge the effects of deprivation on a transmitter system which is intrinsic to the bulb, while norepinephrine (NE) concentrations were assessed to determine how deprivation affects inputs to the bulb from higher brain regions. A significant reduction in DA concentration (pg/mg protein) was observed on Day 8 and persisted until Day 30 although protein concentrations (pg/mg bulb) were not affected. In contrast, deprivation did not significantly alter NE concentration. Deprived and control pups did not differ on a series of behavioral and morphometric measures, suggesting that the surgical procedure did not seriously impair normal growth patterns. The results indicate that unilateral naris occlusion induces rapid and specific changes within the olfactory bulb.