We investigated the effects of dopamine and its agonists and antagonists on the receptive field properties of ganglion cells in the isolated eyecup preparation of the rabbit. In general, dopamine (20-250 microM) reduced the overall sensitivity of ganglion cells to light stimuli while increasing the spontaneous activity of off-center cells and decreasing the spontaneous activity of on-center cells and on-off directionally selective cells. Neither(-)-apomorphine (8-82 microM) nor the selective D-2 agonist LY 141865 (7-85 microM) mimicked the effects of exogenous dopamine. Instead, both drugs altered the responses of ganglion cells in a manner similar to that of the selective D-1 antagonist SCH 23390. The latter at 4-41 microM: (1) selectively reduced the antagonistic surround responses of off-center cells; (2) changed the sustained excitatory responses of on-center sustained cells to spots of light into sustained inhibitory responses; (3) selectively reduced the leading edge responses of on-off directionally selective cells to moving light stimuli, and (4) decreased the spontaneous activity of off-center cells while increasing the spontaneous activity of on-center cells. The effects of the selective D-2 antagonist S-sulpiride (37-116 microM) on the responses of on-center cells resembled those of exogenous dopamine, while for off-center cells the effects of S-sulpiride were similar to those of (-)-apomorphine and LY 141865. Results were compared with those obtained previously with dopamine antagonists haloperidol, fluphenazine and cis-flupenthixol on ganglion cell responses in the intact rabbit eye. These three drugs were clearly acting at D-1 receptors. The present findings support a physiological role for D-2 receptors in visual processing in the rabbit retina, in particular the hypothesis that endogenous dopamine release is modulated by inhibitory D-2 autoreceptors. They also suggest that one function of dopaminergic neurons may be to modulate the sensitivity of ganglion cells to light stimuli.