A prolonged weak illumination has been reported to induce an off-response in transretinal potential of bullfrog retina immersed in a low Ca2+, Ba2+ and Na-aspartate-containing solution. Changes in the interstitial current accompanying the generation of the off-response were studied by inserting a pair of micropipettes into the bullfrog retina. A transient increase in proximal-to-distal current above the dark level was observed when the off-response was developing (off-current). The current divergence of the off-current indicated that the source of the off-current was located about 75 micron below the receptor surface. In the absence of Ba2+, similar changes in currents were also observed, although no detectable off-response was observed in the transretinal potential. Findings suggest that regardless of the presence of Ba2+, current flowing outward through the plasma membrane of the rod inner segments increases transiently when the off-response is developing.