We have developed two mouse monoclonal antibodies, M912-2A2 and M912-2G10, against cell surface antigens of a human infantile embryonal carcinoma cell line, MTE. The distribution of these antigens (designated as 2A2 and 2G10) was almost identical in human germ cell tumors in which they hallmarked yolk sac components and some tubular endodermal structures. Immunoelectron-microscopically, the antigens were located on the microvilli of MTE tumor cells. These antigens were not found on other common childhood tumors. In normal and fetal tissues they exhibited quite different distributions. In the kidney, 2A2 and 2G10 were present on the collecting tubules and proximal/distal tubules, respectively. Expression of both antigens was already observed in fetal kidneys of 10 weeks gestational age. In hematopoietic cells 2G10 was present only on granulocytes and on erythrocytes regardless of ABO blood group, whereas 2A2 was not present on any peripheral blood cells. Both antigens were equally expressed in testis and epididymis. Biochemically, reactivity of both antibodies was abolished with periodate treatment, suggesting their carbohydrate nature. Further biochemical characterization revealed that antibody to 2G10 reacts with the nonreducing terminal structure of type 2 carbohydrate chain, Ga1 beta 1-4G1cNAc, common to nLc4 (paragloboside), nLc6 (neolactohexaose), and Y4 neutral glycolipids of O-type erythrocytes. These data illustrate the complexity of carbohydrate antigens on yolk sac components of human germ cell tumors and provide a basis for the study of primitive endodermal and yolk sac differentiation in these tumors.