An investigation of poliomyelitis was undertaken at the South African Institute for Medical Research in collaboration with the Public Health Department, Johannesburg, and the Union Health Department. It was shown that the common South African vervet monkey Cercopithecus aethiops pygerythrus is susceptible to the virus of poliomyelitis, and suitable for the study of the disease. The distribution of the virus in a small children's home in which a case of poliomyelitis had occurred was studied. It was shown that two of seven healthy contacts were excreting the virus in their faeces. One of these contacts still excreted the virus one month after its presence was first detected, but no virus was detected two months later.