Dopamine is generally considered to be an inhibitory neurotransmitter in the central nervous system. Dopamine release in the nucleus accumbens can be evoked by chemical stimulation of the afferent cell bodies using N-methyl-D-aspartate microinjection in the ventral tegmental area. We report here that following such injections most neurons of the nucleus accumbens were excited. This excitation was abolished if dopaminergic neurons were lesioned and was blocked by antagonists of the D1 dopamine receptors. Finally, excitatory responses to electrical stimulation of the hippocampus were strongly facilitated by endogenously released dopamine. We suggest, therefore, that under physiological conditions, dopamine acting on D1 receptors is actually an excitatory neurotransmitter.