Sex steroids exert multiple functions in the central nervous system. They modulate responses to olfactory information in mammals but their participation in the regulation of neurotransmission in the olfactory bulb is unknown. We studied by Western blot the effects of estradiol (E2), progesterone (P4), and allopregnanolone (Allo) on the content of glutamic acid decarboxylase (GAD), gamma-aminobutyric acid A receptor alpha-2 subunit (GABA(A)R alpha-2), glutamate receptor 2/3 (GlutR 2/3), and tyrosine hydroxylase (TH) in the olfactory bulb of gonadectomized male rats. GAD content was increased by all steroids administered alone. Interestingly, progestins reduced E2 effects on GAD content. Steroids increased the content of TH and GABA(A)R alpha-2. In contrast, GlutR 2/3 content was decreased by E2 and P4, whereas Allo did not modify it. These results suggest that estrogens and progestins regulate olfactory bulb functions in the male rat by modulating the expression of key proteins involved in several neurotransmission systems.