In order to establish the usefulness of the human tumor-nude mouse system as a predictive screen for anticancer agents, 17 tumors (3 breast, 3 colon, 3 lung, 3 melanoma, 2 ovary, 1 prostate, 1 sarcoma, and 1 larynx), serially transplantable in athymic mice, were used to study antitumor activity of doxorubicin (Adriamycin). BALB/c nude mice were treated i.v. on a weekly basis for 3 to 4 weeks, starting when the tumor volume became relatively large (advanced stage of tumor treatment). All the tumors except lung tumor T 293 showed a 90 to 100% take rate and stable growth. Doxorubicin, at dose levels of 6 and 10 mg/kg/injection i.v. every week for 3 weeks, showed significant activity against all of the three breast tumors studied. As was expected on the basis of clinical data, doxorubicin showed no antitumor activity against the three different colon tumors. In the case of lung tumors, statistically significant activities against oat cell carcinoma T 293 and epidermoid carcinoma T 222 were observed. In contradiction to clinical data, doxorubicin was found to have significant activity against various melanomas studied and slight but not statistically significant activity against ovarian tumor T 17. Experimental results obtained using doxorubicin against prostate, sarcoma, and larynx tumors also parallel the reported clinical data.