P-glycoprotein (P-gp) and multidrug-resistance protein-1 (MRP-1) are adenosine triphosphate-binding cassette proteins that may decrease intracellular concentrations of anti-human immunodeficiency virus (HIV) drugs. After HIV-1(IIIB) infection, HIV-1 protein and infectious virus production were decreased by at least 70-fold in CEM cells overexpressing P-gp but were increased by at least 50-fold in CEM cells overexpressing MRP-1, compared with control CEM cells. After transfection with the HIV-1(IIIB) genome, cells overexpressing P-gp and MRP-1 expressed similar amounts of HIV protein. Selective inhibitors of MRP-1 and P-gp partially reversed the effect of these transporters in a concentration-dependent manner. P-gp preferentially associated with glycolipid-enriched membrane (GEM) domains, which may be an important site for cellular binding and egress of HIV. In contrast, MRP-1 was not preferentially found in GEM domains. These results suggest that the inhibition of HIV productive infection by P-gp and augmentation by MRP-1 occur predominantly at a preintegration step but act through different mechanisms.