We recently purified a 200 kD peanut agglutinin-binding glycoprotein from the embryonal carcinoma cell line HT-E (833K) that is expressed selectively in nonseminomatous germ cell tumors. We now further characterize gp200 using Western blot analysis to compare normal and malignant testicular germ cells for reactivity to peanut agglutinin, a plant lectin that recognizes terminal D-galactosyl residues, and GCTM-2, a monoclonal antibody that recognizes a 200 kD keratan-sulfate proteoglycan on human embryonal carcinoma. The results indicate that normal germ cells express gp200 as a membrane-bound 230 kD glycoform that expresses terminal galactose residues. This 230 kD glycoprotein is absent on spermatozoa but present on seminomatous germ cell tumors and somatic tissue and does not express terminal galactose on its carbohydrate side chains. In contrast, nonseminomatous germ cell tumors express a heavily sialylated glycoform of gp200 that does express terminal galactose residues. These results describe a glycoprotein that exists in several glycoforms in normal and malignant testicular germ cells. The differential expression of these glycoforms may help in understanding the ontogeny of germ cell tumors.