1. The fish EIRG (Svaetichin's cone action potential) was investigated on Cyprinus auratus with several types of illumination.
2. The response amplitude depended strongly upon the area illuminated, becoming very small when the diameter of light spot was decreased to 0.2 mm.
3. During passage of the border of light and dark across the site of recording, no abrupt change occurred in the response amplitude.
4. Illumination by monochromatic light whose wave-length was changing continuously through the visible spectrum produced various response curves from different regions of the same retina. The result appeared to confirm Svaetichin and Motokawa et al., but details could not be compared due to the difference in experimental conditions.
5. Based on the above results, the nature of the response was discussed.