differential inhibitory effects of sulfated polysaccharides and polymers on the replication of various myxoviruses and retroviruses depending on the composition of the target amino acid sequences of the viral envelope glycoproteins sulfated polysaccharides ie dextran sulfate and sulfated polymers ie sulfated polyvinylalcohol and sulfated copolymers of acrylic acid with vinylalcohol were found to be potent and selective inhibitors of the replication of respiratory syncytial virus rsv and influenza virus type a influenza a virus but not of other myxoviruses parainfluenza 3 measles and influenza b viruses the compounds were also inhibitory to human immunodeficiency virus type 1 hiv1 and hiv2 and simian immunodeficiency virus but not simian aidsrelated virus the mode of antiviral action of the sulfated polysaccharides and polymers can be attributed to an inhibition of virus binding to the cells hiv1 inhibition of viruscell fusion influenza a virus or inhibition of both viruscell binding and fusion rsv the fact that the sulfated polysaccharides and polymers are inhibitory to some myxoviruses and retroviruses but not to others seems to depend on the composition of the amino acid sequences of the viral envelope glycoproteins that are involved in viruscell binding and fusion all myxoviruses and retroviruses that are sensitive to the sulfated polysaccharides and polymers share a tripeptide segment pheleugly this tripeptide segment may be involved either directly as a target sequence or indirectly in the inhibitory effects of the compounds on viruscell binding and fusion