This review is a concise description of the study undertaken to examine the modulation by opioids of simian acquired immunodeficiency syndrome (SAIDS) induced by inoculation of rhesus monkeys with simian AIDS virus SIVmac239. The study showed that the replication rate of the virus was several times greater in monkeys made dependent on morphine than in those of non-morphine treated monkeys. Further, a significant change in the mutation rate of the infecting virus in morphine-treated monkeys resulted in the production of mutants that were silent to conventional serological screening tests as well as resistant to AZT. In addition, opioid and chemokine receptors involved were identified in immune cells and a full comparative spectrum of the compromise of the immune system was examined allowing subsequent studies to evaluate wherein the modulation of the development of the syndrome could be better characterized. The data gathered to date are unique and germane to furthering our understanding of AIDS in humans and its subsequent treatment thereof.