In vivo screening models of a cisplatin (CDDP)-resistant human small-cell lung cancer cell (SCLC) line, H69/CDDP, and a non-small-cell lung cancer cell (NSCLC) line, PC-14/CDDP, were evaluated. The transplantability of the tumor xenografts to SCID mice was more than 90%. Tumor xenografts of H69/CDDP and PC-14/CDDP showed CDDP resistance during in vivo treatment. The novel anticancer agent 254-S showed only a partial effect on the growth of H69/CDDP and PC-14/CDDP while ormaplatin showed no cross resistance to CDDP. The in vivo results correlated well with the results of the in vitro MTT assay. In this in vivo sensitivity test, H69/CDDP and PC-14/CDDP were more sensitive to ormaplatin than its parental cell lines. In vivo sensitivity testing using SCID mice bearing transplanted CDDP-resistant tumors was shown to be useful for evaluating the effects of new anti-cancer drugs, especially those that might overcome CDDP resistance.