The effects of the unilateral olfactory naris closure were studied immunohistochemically in the main olfactory bulb of adult rats. In the olfactory deprived bulbs, the tyrosine hydroxylase-immunoreactive elements in the glomeruli and the juxtaglomerular region decreased drastically, whereas the glutamate decarboxylase-immunoreactive elements in these regions showed no appreciable changes, indicating the differential effects of olfactory deprivation on catecholaminergic and GABAergic traits in spite of their coexistence in some neurons in these regions.