Macaca mulatta retinas were superfused, in vitro, to measure the efflux of dopamine. Steady light, in the low photopic range, stimulated dopamine release slightly. Flashing light (3 Hz) superimposed over the steady background increased dopamine efflux significantly. This increase was completely blocked by the addition of d,1-2-amino-4-phosphonobutyric acid (d,l-APB, 10-100 microM) to the superfusion medium, but not by the addition of the inactive enantiomer d-APB (10 microM). The results suggest that ON bipolar cells provide the excitatory drive to dopaminergic amacrine cells in primates, as in other species.