A type D retrovirus isolated from a permanent human cell line (PMFV) was employed as diagnostic reagent both in Southern transfer hybridization experiments using the cloned genome as a probe and in immunoblot analysis using SDS disrupted virus particles. Hybridization experiments performed under conditions of different stringencies revealed a close homology of PMFV to SAIDS type D retroviruses of serotype 1 (SRV-1, SAIDS retrovirus D/NE), a related homology to the prototype type D virus (MPMV) and to viruses of serotype 2 (SRV-2), but no homology to the endogenous type D retrovirus of squirrel monkeys (SMRV) and the human AIDS virus (HIV-1). Antigens of PMFV showed cross-reactivity only to antibodies of a SAIDS infected macaque, but no reaction to anti HIV-antibodies of seropositive patients. Thus, the type D virus isolated from a human cell line and closely related to SAIDS type D viruses of macaques is not related to the AIDS virus in humans.