Abstract Spectral sensitivity of rhesus monkeys was determined before and after the total ablation of the superior colliculi. The hypothesis tested was that photopic spectral sensitivity would not be affected by the colliculectomy whereas the monkeys would loose scotopic sensitivity. This hypothesis was derived from the fact that photopic sensitivity is abolished in destriate monkeys and the remaining visual centers, probably the superior colliculi, only manifest scotopic sensitivity. Four normal and four colliculectomized monkeys were tested psychophysically to determine their photopic and scotopic spectral sensitivity. The results indicate that not only the control but also the experimental group have normal photopic and scotopic spectral sensitivity, thereby infirming the working hypothesis. These results are interpreted as indicating that, whereas the subcortical visual areas receive purely rod input, the geniculo-striate visual system is probably a mixed system receiving both rod and cone inputs.