The interaction of human red blood cells carrying antihuman collagen antibody with collagen-coated surfaces was studied. Avidin was used as bifunctional crosslinking agent for the attachment of antibody to the red blood cell surface. Antibody-carrying red blood cells efficiently and specifically bound to collagen-coated surface covering a significant part of the surface. The components of normal blood had an insignificant effect on red blood cell binding. A model of drug targeting to the injured sites(s) of blood vessel wall is proposed.