Electrocortical responses were studied in kitten ranging from 4 to 56 days of age. From 4 to 10 days only a long-latency negative wave was present; from 10 to 20 days 2 separate responses were present, a short-latency positive-negative complex and the long-latency negative wave; by 30 days of age the latter coalesced with the former. Lesions of the superior colliculus, pretect-um and brachlum of the superior colliculus abolished or markedly reduced the long-latency response but did not affect the short-latency response. Lesions of the lateral geniculate nucleus eliminated the short-latency response, but left the long-latency response unaffected. The short-latency response is identified as a specific visual response and the long-latency response as a nonspecific visual response. Possible developmental correlations have been discussed in terms of morphological, electrophysiological, and behavioral changes as a function of age.