Mesencephalic dopaminergic neurons were electrophysiologically identified by a variety of criteria, including antidromic activation from prefrontal or cingulate cortex, neostriatum, or nucleus accumbens in urethane-anesthetized rats. The mean firing rate of 98 mesocortical dopaminergic neurons was 2.9 +/- 0.3 spikes/sec and did not differ from the mean firing rate found for nigrostriatal or nucleus accumbens dopaminergic neurons. Spontaneously active mesocortical dopaminergic neurons were inhibited by intravenous administration of either apomorphine (6 micrograms/kg) or amphetamine (0.25 mg/kg). Whereas most antidromic responses of nigrostriatal and mesoaccumbens neurons consisted of the initial segment spike only, cortically-elicited antidromic responses typically consisted of a full initial segment-soma-dendritic spike. These findings are discussed with regard to the presence of soma-dendritic autoreceptors on mesocortical dopaminergic neurons.