Hemin, a critical component of hemoglobin, is an active ingredient of a biologic therapeutic approved by the Food and Drug Administration for the treatment of acute porphyries. This report describes a biological function of this molecule in inducing host defense against HIV-1 infection via heme oxygenase-1 (HO-1) induction. Treatment of monocytes with hemin substantially inhibited HIV replication, as evident by nearly undetectable viral RNA and cell-free HIV-1 p24 protein in a dose-dependent manner. Hemin exposure of these cells before infection, at the time of infection, or after infection caused> 90% reduction of HIV DNA with substantially low levels of HIV-1 p24 and HIV-associated cytopathic effects. In addition, hemin treatment significantly suppressed infection of both monocytes and T cells inoculated with R5, X4, R5X4 tropic strains, and reverse transcriptase-resistant, azidothymidine-resistant, ddC/ddI-resistant, nivirapine-resistant, and other clinical HIV isolates. Intraperitoneal administration of hemin 4 days after HIV infection reduced viral load in the serum of human PBMC-reconstituted nonobese diabetic SCID mice by> 6-fold. Suppression of HIV replication in hemin-activated cells correlated with the induction of HO-1 and was attenuated by tin protoporphyrin (SnPP) IX, an inhibitor of HO-1 activity, suggesting a pivotal role of this endogenous enzyme in the regulation of HIV infection. Hemin-induced HO-1 induction in the CCR-5, CXCR-4, and CD4 coexpressing GHOST (3) cells was consistent with the inhibition of Tat-dependent activation of long terminal repeat promoter leading to reduced GFP expression. These findings suggest an important role of hemin-induced HO-1 activity as a host defense mechanism against HIV-1 infection.