As more is learned about the human immunodeficiency viruses HIV-1 and HIV-2, increasingly sophisticated methods of acquired immunodeficiency syndrome (AIDS) treatment and prevention may be implemented. Integral to an understanding of these viruses is an analysis of both the viral antigens and the host-immune responses to these antigens, which may differ from HIV-1 to HIV-2. Because levels of both antigen and antibody vary throughout disease development, knowledge of how and why such changes occur will lend insight into viral pathogenic mechanisms and will facilitate the development of differential diagnostic tests for classifying AIDS patients and their disease states. This task becomes very complex when dealing with HIV viruses because they possess an unprecedented number of regulatory genes for members of the retrovirus family.