Although human tumor xenografts have been extensively used for preclinical evaluation of antitumor agents, most of this work has utilized subcutaneous or subrenal capsule assays based on change in tumor size. To obtain experimental models more reflective of the human clinical situations, we have developed several metastatic models that are based on and complement a panel of cell strains used in large-scale in vitro drug screening. One melanoma and four lung tumors produced metastatic lesions in the lung within 60 days following subcutaneous, intraperitoneal, or intrasplenic inoculation of BALB/C athymic nude mice. Several tumors also produced liver lesions, and one lung tumor strain showed metastasis to the brain. The metastatic lesions histologically resembled the tumors that grew at the inoculation site. In vitro and in vivo cell strains were rederived from the metastatic lesions. These systems may provide practical models for experimental drug and immunotherapeutic trials.