Retinal evoked responses to sinusoidal gratings modulated in counterphase (pattern ERG) have been recorded from the pigeon eye. The pattern ERG amplitude depends upon the temporal frequency of the modulation, the contrast, the spatial frequency and the area of the stimulus. In 8 pigeons the pattern ERG has been recorded at different times after the unilateral section of the optic nerve. It has been found that the pattern ERG has a comparable amplitude in the two eyes as a function of the spatial frequency, 3 and 9 months after the section of the left optic nerve. At these times, histological evidence shows a drastic reduction in the density of the retinal ganglion cells on the operated side in comparison to the control one. These findings suggest that retinal sources other than the ganglion cells are responsible for te generation of the pigeon pattern ERG.