The inhibition of HIV-1 replication in vitro by Immunor 28 (IM28), an analog of dehydroepiandrosterone (DHEA), was monitored using the HIV-1 laboratory wild-type strain IIIB. Evaluation of the 50% inhibitory dose (IC50) revealed a decrease in HIV-1 replication giving an IC50 value around 22 microM. The toxicity of the drug has been determined also, in MT2 cells and PBMCs. 60 microM of IM28 provoked a 50% decrease in cell viability while DHEA caused the same decrease at 75 microM in MT2 cells. These values are 125 microM for IM28 in PBMCs and 135 microM for DHEA. Thus, DHEA is less toxic than IM28, but IM28 has a higher antiviral activity.