Peripheral deafferentation of the mouse main olfactory bulb following intranasal irrigation with ZnSO4 produced profound decreases in tyrosine hydroxylase activity and immunoreactivity in intrinsic dopamine neurons normally localized to the juxtaglomerular region of the bulb. In contrast, only modest alterations in GABA-immunoreactivity and glutamic acid decarboxylase (GAD) activity were observed in the same region. In fact, when GAD activity was expressed per mg tissue, a reflection of enzyme concentration, no changes in activity were observed 3 weeks postlesion and only relatively modest decreases in specific activity were found following long survival times (4 months). When the data were expressed per bulb, as an indication of the total amount of enzyme present, GAD activity and bulb weight exhibited similar reductions. Olfactory marker protein levels, determined as an indication of the completeness of the deafferentation, were at or below the limits of detection in all lesioned mice. These data indicate that afferent regulation of transmitter expression in the juxtaglomerular neurons of the olfactory system is phenotype specific.