Summary: The effect of the route of immunization on the response of rabbits to BSA in Freund adjuvant has been studied. Intramuscular and subcutaneous injection gave the highest circulating antibody levels, toe pad and intraperitoneal injections were intermediate, and intradermal and intravenous injections were least effective. The toe pad and intradermal routes were most effective for production of delayed hypersensitivity; the intramuscular, subcutaneous and intraperitoneal routes were less effective, and the intravenous completely ineffective. An intravenous booster injection suppressed delayed hypersensitivity in all cases and caused significant increases in circulating antibody in animals inoculated by the intraperitoneal, intradermal, intravenous, and toe pad routes.