Abstract A high percentage of baboons of the species Papio papio have presented evidence of photomyoclonic epilepsy (2, 3 and 4). Four of the first group of 10 from Senegal (tested in the laboratories of Dr. R. Naquet, C.N.R.S.-I.N.P. 3, Marseille, France) presented characteristic clinical and electroencephalographic signs of the syndrome (2). Later, a series including 40 animals of similar origin was described (3) in which 24 of 40 showed EEG and motor paroxysmal responses on the first test and 5 additional showed the syndrome on subsequent tests. A study of 100 Papio papio in Dakar and at the supplier's station in Kaolack, Senegal, revealed that the first exposure to light flickering at the critical frequency resulted in abnormal paroxysmal activity in 60% of the animals which had no history of dietary change, shipping stress, pharmacological intervention and the like (4). The present study represents an investigation into the inherent nature of this photosensitivity in the baboon by analysis of response to flickering light of randomly selected animals from a closed colony of Papio papio maintained at the Southwest Foundation for Research and Education and interbred through generations over a period of 20 years in captivity. These were compared to baboons of two other species (Papio anubis and Papio cynocephalus) living in the same environment in San Antonio but of African origin. The animals were made available through the courtesy of Drs. Harold Vagtborg, director of the Foundation, and Robert Hummer, Director, Division of Animal Resources.