The antiviral activities of various interferon preparations against human immunodeficiency virus (HIV) were evaluated in vitro. Recombinant interferon alpha-A, and beta interferons and leukocyte-derived alpha interferons show similar concentration-dependent antiviral activity. Recombinant and lymphocyte-derived gamma interferons show minimal antiviral activity against HIV replication in normal peripheral blood mononuclear cells, but definite activity against HIV in the H9 lymphocytic and U937 monocyte-macrophage cell lines.