We have studied the expression of both HLA class and the recently described HLA class I-like genes (HLA-E and HLA-6.0) in two human developmental tumor cell lines, that serologically could not be typed for HLA-A, -B, and -C. Evidence is presented that the teratocarcinoma Tera-2 stem cells express trace amounts of non-beta 2 microglobulin-associated classical HLA-A, -B, and -C Ag on their cell surface.