1. Dopamine modulation of gamma-aminobutyric acid (GABA)-elicited currents was studied in cone horizontal cells acutely isolated from the catfish retina using the whole-cell patch-clamp technique. 2. GABA puffs elicited both a GABAC current and a transporter current. Dopamine (10 microM) in the bath selectively reduced the GABAC receptor current without affecting the GABA transporter current. 3. This effect of dopamine was mimicked by the D1 agonist SKF38393 (25 microM) and an adenylyl cyclase activator forskolin (20 microM) but blocked by the dopamine antagonist haloperidol (30 microM). 4. These findings provide the first evidence for dopamine modulation of GABA receptor function in the vertebrate nervous system. In the intact retina, dopamine may modulate GABA-mediated chemical coupling and autofeedback in horizontal cells.