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The double b-wave component, which is clearly evidenced during pentobarbital infusion, has been reported by Witkovsky (1963) and Scholes and Roberts (1964) in the hatched chick. They suggested that these waves thought to represent photopic and scotopic activities. The author also observed these waves in the young chick (Ookawa, 1971), and confirmed that the first component has photopic response properties and the second has scotopic characters, as herein reported. Nine male White Leghorn chicks (Goto-201 line), age 15 to 16 days after hatching, were used. The method of recording ERG was described in the previous paper (Ookawa, 1971). The ERG was recorded with a dual-beam oscilloscope using a time constant of 1.0 second. An upward displacement in the record was taken as positive for corneal electrode. An xenon flash (Nihon-Koden, MSP-2R) was used for a photostimulus. The distance between the photostimulator and the eye was about 70 cm. The energy…