In the early 1980s, an unusual clustering of lymphomas and immunodeficiency-associated disorders was noted in a colony of captive macaques at the New England Regional Primate Research Center (South-borough, Massachusetts, USA)[1–3]. These observa-tions eventually led to the isolation of a new group of T-cell tropic retroviruses, now called simian immuno-deficiency viruses (SIV)[4]. SIV from macaques (SIV,..), was found to be antigenically related to HIV and preferentially grew in CD4+ T-cells in culture. Ex-perimental inoculation of rhesus macaques (Macaca mulatta) with SV „resulted in immunodeficiency and death from opportunistic infections, thus estab-lishing the SIV model of AIDS [5].

Since that time, distinct but related lentiviruses have been isolated from a number of African non-human primate species, and many more are apparently infected as determined by serological testing. Our current understanding of the relationship between these non-human primate lentiviruses and HIV-1 and HIV-2 suggests that the ancestors of the human viruses were probably members of a large family of lentiviruses resident in African non-human primates for many cen-turies [67]. The best current evidence for such a re-lationship is found in the data linking SIV from sooty mangabeys (SIV „) to HTV-2 in West Africa [89].