Fifteen monoclonal antibodies (mAb) that show specificity for human embryonal carcinoma cells are described. C57BL/6 mice were immunized with Tera-2 embryonal carcinoma cells, and hybridomas were isolated and tested versus a set of human developmental tumor cell lines. The antigens exhibit relatively restricted and unique distributions on normal tissues as shown by immunohistochemistry. The mAbs recognize a series of differentiation antigens since their expression changes when teratocarcinoma stem cells are induced to differentiate in vitro. The expression of these molecules in germ cell and related tumors is consistent with the data obtained from in vitro cell studies. Seven of these mAbs immunoprecipitate molecules from surface labeled Tera-2 cells that show distinct molecular weights on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The antigenic phenotypes defined by the set of mAbs can be used to investigate possible pathogenetic relationships of the various testicular tumors.