The HVJ-mediated interaction of liposomes containing glycophorin with human erythrocytes was studied. A ternary complex of erythrocyte-HVJ-liposome was formed on incubation at 4 degrees C. Spin-labeled phosphatidylcholine and spin-labeled galactosylceramide, both of which were incorporated into liposomes, were effectively transferred into erythrocytes upon shifting-up of the incubation temperature to 37 degrees C. This finding indicates that fusion between glycophorin liposomes and erythrocytes occurs in the presence of HVJ. Fusion could be also inferred from the transfer of radio-labeled lipids embedded in the liposomal membranes to erythrocyte membranes as well as uptake of solutes entrapped in the aqueous space of the liposomes by erythrocytes. The total amount of liposomes fused with erythrocytes depended on the glycophorin content of liposomes and the amount of HVJ added. No transfer was observed when trypsinized HVJ was used in place of HVJ, suggesting that the fusion is F protein dependent.