Spectral curves were derived for cells isolated in the optic tectum of turtle. All cells were most sensitive to the red region of the spectrum with some cells showing a secondary peak in the blue-green region. The majority of cells showed an on-off response to wide field stimulation. Spectral plots for on and off responses showed antagonistic inputs from spectrally different receptor processes. These results suggest that the optic tectum in the turtle is capable of processing intensity and wavelength information.