In infected human cells, nitric oxide (NO) has been shown to inhibit the replication of the human immunodeficiency virus-1 (HIV-1), the etiological agent of AIDS. Evidence suggests that NO may regulate HIV-1 replication by affecting the sulphydryl redox state. In this respect, it has been very recently demonstrated that NO-donors inactivate the HIV-1-encoded protease and reverse transcriptase in vitro. Further viral and host NO targets may be envisaged. Although no data are available on the anti-HIV-1 effect of NO in vivo, NO-releasing drugs, clinically used in the treatment of cardiovascular disorders, may represent a novel class of molecules for decreasing virus replication. Here, the possible molecular bases for the anti-HIV-1 effect of NO are discussed.