Rats without visual cortex and control rats were trained to make a lightdark discrimination in a Skinner box. In agreement with previous investigations with eats, the rats without striate cortex exhibited an impairment at low light intensities. In contrast to the previous experiments with cats, however, it could not be concluded that the absolute threshold to light is directly affected by removal of visual cortex. The consequences of visual cortex removal on retention of the light-dark discrimination habit were also investigated and were found to have little or no effect.