ERG c-waves were recorded from eyes of anesthetized chickens by stimulating with monochromatic bright light ranging from 460 to 620nm, under yellow or red light adaptation, using various energy levels i.e. 1, 3, 4 and 5W/m2 at the corneal surface in the former, and 3, 4 and 5W/m2 in the latter. After recording a series of c-waves, the spectral sensitivity curve for each adaptation condition was obtained. Amplitude-intensity curves showed that amplitudes increased with increment of stimulus luminance. The energy required to release a response of a given criterion magnitude was determined at each of the wavelengths investigated. The peak wavelength of the spectral sensitivity curve of the c-wave under both yellow and red light adaptation was 520 or 540nm both of which were shorter than the peak wavelength (560nm) under white light adaptation. These results showed that under the yellow and red light adaptation the sensitivity of the c-wave response to monochromatic light in the longer wavelength range was suppressed, suggesting the possibility of isolating cone-mediated c-wave response. A peak (520 or 540nm) and a shoulder (580nm) in the spectral sensitivity curves were presumed to be derived from two types of cone systems.