Immunization to B16 melanoma is known to induce tumor-specific immune responses, yet the identity of the immunogenic antigens on these cells is not known. To answer this question, sera obtained from mice immunized to a partially purified B16 melanoma antigen vaccine that induced tumor-protective immunity were used to immunoprecipitate extracts of radioiodinated B16 melanoma cells. Immunogenic antigens were identified by sodium dodecyl sulfate polyacrylamide gel electrophoresis and autoradiography of immunoprecipitates. Though the vaccine contained a number of different components, only three induced antibody responses in syngeneic mice. These antigens were surface proteins with molecular weights of approximately 90, 200, and 250 + kDa. The three antigens were expressed by B16F1, B16F10, and B16F106-Lr melanoma cell variants but not by several unrelated syngeneic or xenogeneic cancers or by normal murine tissues. Thus, we have been able to identify some of the antigens in B16 melanoma that are immunogenic in syngeneic mice.