The immunopotentiating action of BCG and wax D was comparatively evaluated as the immune response to sheep red blood cells (SRBC) in mice. The immunopotentiation of BCG varied with the interval between its priming and subsequent antigen injection. BCG increased delayed type hypersensitivity (DTH) at early stage but enhanced antibody formation at later stage. DTH reached its maximum about 5 weeks after BCG inoculation. In contrast, wax D increased antibody formation at early stage but increased DTH at later stage. Freund complete adjuvant (FCA) containing wax D stimulated much antibody formation rather than induction of DTH in mice. Cord factor and even Drakeol 6VR could induce DTH at early stage of prior inoculation.