Between November 1979 and July 1982, 7 captive gelada baboons (Theropithecus gelada) died; 5 of them died unexpectedly, 1 died after a 4-month history of heart failure, and 1 was anemic and dyspneic for 2 days before death. Of those that died unexpectedly, 1 was anemic and 4 were clinically normal. At necropsy, all baboons had white or pale patches of myocardium. Histologically, fibrosis and acute myocytolysis were observed in the myocardium. Three affected baboons were tested for plasma alpha-tocopherol content and were found deficient. Four unaffected baboons were given vitamin E for 24 months, and plasma alpha-tocopherol content returned to normal. Blood selenium content was determined in 1 affected baboon and was normal.