The inhibitory effects of several polysaccharides, dextran, xylofuranan, and ribofuranan, and their sulfated counterparts on the infectivity and replication of human immunodeficiency virus (HIV) were examined by using an HTLV-I-carrying cell line, MT-4, in vitro. Dextran sulfate (Mw 34 X 10(3], xylofuranan sulfate, and ribofuranan sulfate completely prevented HIV-induced cytopathic effects (CPE) at concentrations greater than 10 micrograms/ml and dextran sulfate (Mw 7 X 10(3] at concentrations greater than 100 micrograms/ml. However, the non-sulfated compounds did not prevent them at any concentration tested. The anti-HIV effect of these polysaccharides was confirmed by measuring HIV-specific antigen expression in infected MT-4 cells. In cocultures with MOLT-4 and MOLT-4/HIVHTLV-IIIB cells, formation of multinucleated cells was completely inhibited in the presence of 100 micrograms/ml of these sulfated compounds. Dextran sulfate showed 20-30% growth inhibition of uninfected MT-4 cells at 1000 micrograms/ml but dextran sulfate, xylofuranan sulfate, and ribofuranan sulfate showed no effect on sulfated polysaccharides efficiently inhibited the reverse transcriptase activity of avian myeloblastosis virus and HIV.