HIV2 infections at present, are predominantly found in west Africa where it is the dominant form of HIV. Both HIV1 and HIV2 have the same modes of transmission and are associated with similar opportunistic infections and AIDS. In persons infected with HIV2, immunodeficiency seems to develop more slowly and to be milder, but as the disease advances, HIV2 infectiousness seems to increase. Little is known about the best approach to the clinical treatment and care of patients infected with HIV2. Some drugs used to treat HIV1 are ineffective. HIV1 and HIV2 have similar gag (viral core) and pol (polymerase) regions, they have relatively dissimilar env (envelope) regions. Owing to this lack of homology in the envelope region, there is little serologic cross-reactivity of the antibodies directed against the envelope antigens of both HIV1 and HIV2. The env gp36 ectodomain is highly conserved and elicits a type-specific antibody response. Hence, most licensed diagnostic assays incorporate gp36-derived antigens to detect HIV2 specific antibodies. It is becoming important to differentiate between single infection with either HIV1 or HIV2 and dual infection.