Abstract—The spontaneous efflux of [3H]GABA and its metabolites from the frog retina has been studied. The efflux of radioactivity was multiphasic in the presence or absence of amino‐oxyacetic acid (AOAA), an inhibitor of GABA metabolism, and was not affected by light or dark adaptation.Strong retention of radioactivity was evident in the presence of AOAA, about 90% of the label remaining in the tissue after 4 h superfusion. Under these conditions, increases in the rate of release of radioactivity were evoked by electrical stimulation, 40 mm‐potassium. unlabelled GABA (5 mm), ouabain (5 × 10−5m) and the absence of calcium. The amount of [3H]GABA released by electrical stimulation was not markedly calcium dependent, whereas the response to 40 mm‐potassium was reduced by 96% in the absence