In the late summer of 1967, several patients suffering from a severe disease were admitted to the Department of Medicine of the Marburg University. It soon became obvious that the illness was a hitherto unknown infectious disease. The number of afflicted patients increased to 23. Several cases were observed in Frankfurt/Main at the same time and, some weeks later also in Belgrade, Yugo slavia. Common to all the patients was previous contact with the blood or tissues of Cercopithecus aethiops, the vervet monkey. Altogether 31 people became ill and 7 died. It was soon apparent that the...