Previously, the anti-human immunodeficiency virus type I (HIV-1) activities were reported of four sulfated polysaccharides: dextran sulfate, pentosane polysulfate, chondroitin sulfate, and heparin sulfate. In the present study, the anti-HIV-1 activities of several other sulfated polysaccharides, monosaccharides, neutral polysaccharides, and polypeptides were evaluated. Anti-HIV-1 activities of these various agents were measured by four different assays: (1) HIV-1-induced syncytia formation; (2) infectivity of cell-free HIV-1 after preincubation with the putative anti-HIV-1 agent; (3) protective ability of the agents for target CD4+ cells, and (4) anti-reverse transcriptase activity. In addition, potential toxicity of the putative anti-HIV-1 agents was measured by their effects on cellular proliferation, cytotoxic effects, and effects on coagulation processes. These data indicate that only sulfated polysaccharides and one sulfated monosaccharide, glucosamine 6-sulfate, have significant anti-HIV-1 activity. The therapeutic potentials of these agents are also discussed, with special reference to absorption of glucosamine 6-sulfate through the gastrointestinal tract.