A strong synergistic interaction between the bicuculline-sensitive GABA receptor (GABAAreceptor) and the strychnine-sensitive glycine receptor was observed in third-order neurons acutely isolated from crucian carp retina, with the use of the whole-cell patch-clamp recording technique. In 58 of 153 cells, 10 μM GABA or glycine separately applied to amacrine/ganglion cells failed to induce any responses or only induced small currents (< 20 pA), while co-application of these two chemicals resulted in much larger responses (403.05 ± 319.98 pA). The current induced by the co-application was mediated by chloride channels, and both GABAAand glycine receptors were involved in the potentiation. The underlying mechanisms of this interaction and its possible physiological role are discussed.