An investigation of SA-11 rotavirus binding to human serum lipoproteins was carried out. Various subclasses of lipoproteins, purified by ultracentrifugal flotation, and apoproteins were tested for their activity in inhibiting viral infectivity and hemagglutination. All tested lipoprotein subclasses (very low, low and high density, lipoproteins; VLDL, LDL, HDL, HDL1) were shown to interact with SA-11 rotavirus: VLDL and LDL were the most active in preventing rotavirus replication, whereas HDL and HDL1 inhibited viral hemagglutination to a greater extent. Moreover, A1 and A2 apoproteins were effective towards both viral infectivity and hemagglutination. Results obtained are in agreement with a preferential interaction of VP7 or VP4 proteolytic products with low density lipoproteins and of VP8* with high density lipoproteins. Binding of SA-11 to lipoproteins or apoproteins was also quantified by an enzyme-linked immunosorbent assay procedure and lipoproteins-virus interaction was visualized by electron microscopy.