Glutathione (GSH), its derivatives and N-acetylcysteine (NAC) inhibit the induction of HIV-1 expression in a chronically HIV-1-infected promonocytic cell line (U1/HIV) and peripheral blood mononuclear cells (PBMC). We have examined the effects of GSH and NAC on HIV-1 replication in human primary monocyte/macrophages cultured in vitro. Ficoll-gradient purified human monocytes were cultivated in vitro for 7-10 days and then infected with HIV-1 (Bal and Ada-M). Infection was blocked or substantially reduced by GSH or NAC (5-20 mM). Significant reduction (greater than or equal to 90%) in the amount of virus released, as determined by measuring supernatant reverse transcriptase activity and secreted p24 protein, was obtained when the cells were treated for 4 h with greater than or equal to 10 mM of GSH or NAC. The inhibitory effects of GSH and NAC were concentration dependent. This anti-HIV-1 effect persisted in these cultures for at least 35 days without evidence of significant increase in HIV-1 expression. Thus, a single pulse exposure of HIV-1-infected monocyte/macrophages with GSH or NAC led to a sustained, concentration-dependent decrease in HIV-1 p24 antigen levels, as well as, reverse transcriptase activity without producing detectable cellular toxicity in monocyte/macrophages.