Our surveys indicate that nearly all batches of vervet monkeys arriving at the National Institute for Virology from various areas of South Africa, are infected with foamy viruses and there is evidence that intra-uterine infection also occurs. Monkeys from certain areas of South Africa are apparently infected with the protozoal parasite Entopolypoides macaci in a sub-clinical state which becomes active when the monkeys are splenectomised. Serological studies indicate that infections with schistosomes, tick-bite fever (Rickettsia conori), chlamydsiae and occasionally by leptospirae, occur in monkeys in the Kruger National Park.