The c-wave of the electroretinogram was recorded from the eyes of Dutch rabbits and compared with the slow PIII response isolated by intravenous infection of sodium iodate and intravitreal injection of sodium aspartate. Although opposite in polarity, the waveforms of the two responses were remarkably similar over a wide range of stimulus intensities and durations. Plots of time-to-peak vs. log stimulus energy show that both responses follow the Bunsen-Roscoe law. Curves plotting the locus of all points for which the Bunsen-Roscoe law held were approximately parallel for the two responses, and the critical durations for each stimulus intensity were equivalent. The slow PIII peaked earlier than the c-wave, consistent with published observations that the time-to-peak of light-induced K+ changes is shorter near the photoreceptor inner segments than near the pigment epithelium. These data support the hypothesis that there is a common generator for the c-wave and slow PIII.