Electroretinogram (ERG) and responses of single ganglion cells to 75 microseconds light flashes, applied at two different backgrounds, were studied. Additionally, a stimulation with long-lasting stimuli (ordinarily 5 sec ON-, 5 sec OFF-) was used. Both white and coloured light stimuli were presented. 2. 150 microM 2-amino-4-phosphonobutyrate (APB) was used to separate OFF- from ON- channels. 3. Before APB application, one or two components in the impulse activity in response to a flash were observed, depending on the type of ganglion cell (ON-, OFF- or ON-OFF). the latency of the first component was 60 msec and the latency of the second one was from 160 to 430 msec on average, at different background conditions. APB abolished the first component and enhanced the second one. 4. By means of APB, two components were shown to exist in the main positive wave of the flash ERG. APB abolished the first component and did not influence or enhance the second one. 5. The data obtained show that both ON- and OFF- channels take part in the generation of the frog retinal responses to brief stimuli.
