In 1978--1979, four cases of encephalomyocarditis were recorded in baboons in a simian preserve of the USSR AMS Research Institute of Experimental Pathology and Therapy located in the Zapadnyaya Gumista river valley. The diagnosis was made on the basis of virological and pathomorphological examinations. The isolate recovered from the dead monkeys was identical with the prototype strain of encephalomyocarditis virus (EMC) and the EMC-70 strain previously isolated by us from M. rhesus monkeys. The infection of monkeys caused by the EMC-78/79 virus involved a severe affection of the myocardium of the type of parenchymatous-interstitial myocarditis, moderate encephalitis in the central nervous system, inflammatory changes in the brown fat and cross-striated muscles. An experimental infection in guinea pigs and mice exhibited similar features.