Thirty-seven of 54 human squamous head and neck carcinomas were successfully grown as first transplant generation xenografts under the kidney capsule of conventional mice immunosuppressed by daily treatment with 60 mg/kg of cyclosporine. Of the 18 different tumors evaluated for chemosensitivity, 39% responded to cis-platinum, 19% to 5-fluorouracil, 33% to methotrexate, and 40% to Cis-Pt/5Fu. In comparing the assay results in nine patients who received the same chemotherapeutic drugs, two of three patients responded to their drug with xenograft shrinkage noted, whereas four of six patients who did not respond had tumor growth in the mouse. It is hoped that this model will become useful for new drug testing and, in certain cases, for selection of chemotherapy for patients with refractory tumors.