Factors influencing the time course of S-potentials resulting from brief flashes.

1. Wave forms of the S-potential (luminosity-type) from the tench retina were analysed with single or repetitive flashes.2. In tench the slope of the ;ON' phase was dependent on the relative flash intensity but was independent of flash duration (if it was longer than 15 msec) and the state of adaptation.3. The slope of the ;OFF' phase was a dual function of flash duration and of the state of adaptation. Light adaptation brought forth a sharp ;OFF' phase, referred to as ;cut-off' in this paper.4. Temporal or spatial contrast of light and darkness was necessary for the appearance of the cut-off which was partly responsible for complex wave forms of the L-type potential.5. As far as the wave form is concerned the information on the state of adaptation is well processed before it is fed into the S-space as voltage and does not appear there as a shift in d.c. level.