Infection of macaques by the simian immunodeficiency virus (SIV), like HIV infection in humans, results in a variable time course to clinical disease. Developmental studies of macaques have shown that psychosocial disruption, including social separations, can result in both immediate and long-term immunological consequences. Using colony records on a subset of rhesus macaques (Macaca mulatta) inoculated with SIV at the California Primate Research Center, Davis, California, USA, we constructed regression equations to determine whether the animals' psychosocial histories could explain any of the variability observed in measures of disease progression. After controlling for dosage, age at inoculation, sex, and previous inoculation history, psychosocial variables were found to be significantly associated with several indicators of disease, including latencies to display leukopenia and lymphopenia, weight loss, and survival. We believe these preliminary results suggest an important role for psychosocial processes in affecting disease progression in SIV infection in macaques.