This project will test for the presence of several viral antibodies in adult and juvenile Macacas on Cayo Santiago, Puerto Rico. This has been a closed colony of Rhesus monkeys since 1938. A serological screen carried out in the early 1950's indicated the presence of antibody to SV 40 (46%), herpes B (27%) and measles virus (80%) of the animals in the colony. Three additional antigens have been added to the screen. They are: Rhesus CMV, simian retrovirus D (SRV I) and simian T-Lymphotropic virus type III (STLV III). The objective will be to determine after some 40 years as a closed colony, if herd infection to the three previously studied antigens has been lost and would, therefore, provide an animal population useful for the testing of related strains of viruses. If this colony is shown to be serologically negative for the other three simian viruses, CMV, SRV I and STLV III, then animals from this colony could be used in the study of these simian diseases as models for related human diseases.