A method devised for conjugating liposomes with protein resulted in the binding of up to 200 micrograms of immunoglobulin G per micromole of lipid. The coupling of antibody to human erythrocyte F(ab')2 in vesicles (140 molecules per vesicle) by this method caused a 200-fold increase in the binding of vesticles to human erythrocytes and resulted in about 80 percent of the vesicle lipid and contents being associated with cells.