HIV-1 infection of human PBMC has been shown to elicit secretion of several different cytokines. TNF-α secretion induced by this virus has been of particular interest because it has been associated with the development of HIV-1 dementia and because TNF-α increases viral replication by enhancing NF-κB interaction with the viral promoter, the HIV-1 long terminal repeat. Thus, an autocrine pathway is potentially created in which HIV-1 stimulates its own replication. Conflicting reports exist, however, on the ability of HIV-1 to induce TNF-α secretion in vitro or in vivo. Using experimental protocols that controlled for potential bacterial endotoxin-induced TNF-α secretion, the current study demonstrates significant differences in TNF-α- eliciting properties among primary and laboratory obtained HIV-1. The relative TNF-α-inducing ability of different variants is conserved when tested using PBMC from different individuals. Elicitation of TNF-α secretion was not blocked by exposure of cells to zidovudine, indicating that viral integration was not required to induce secretion. Rather, the interaction between the virus and cell surface is critical for TNF-α induction, as Abs against CD4 or CCR5 blocked the induction of TNF-α synthesis by PBMC when added before virus exposure. Furthermore, the ability to induce TNF-α secretion mapped to a region of the HIV-1 env gene that includes the third hypervariable domain. Differences in the ability of different HIV-1 variants to elicit TNF-α may account for individual differences in HIV-1 disease course.