One hundred and twenty-seven cultured human tumor cell lines produced tumors after sc inoculation of 1-20 million cells into nude mice. They included 56 carcinoma lines, 14 sarcoma lines, and 57 lines from miscellaneous tumors and were all glucose-6-phosphate dehydrogenase type B. Twenty-nine percent of the lines produced tumors of 1 cm3 size within 1 month and 41% in the second month after inoculation. The histopathology correlated with the human tumor of origin in all cases.