Sulphated vinyl polymers such as sulphated polyvinylalcohol, sulphated copolymers of (meth)acrylic acid and vinylalcohol, and pharmaceutically acceptable salts thereof, have an antiviral effect against human immunodeficiency virus and may therefore be used as a therapeutic agent for treating retrovirus infections like AIDS and AIDS-related diseases. Their antiviral activity is apparently based on inhibition of virus adsorption; their inhibitory effect on giant cell formation is stronger than that of dextran sulphate.