The in vitro cytotoxicity of SKI 2053R was evaluated against human tumor cell lines along with those of cisplatin and carboplatin using MTT assay. The cell lines tested were two human lung cancer cell lines and five human stomach cancer celt lines. The level of cytotoxic effects of SKI 2053R against two human lung cancer cell lines was located between cisplatin and carboplatin. However, the cytotoxic activity of SKI 2053R against five human stomach cancer cell lines was similar to that of cisplatin. SKI 2053R is considered to be selectively cytotoxic toward human stomach cancer cell lines. We carried out pharmacokinetic and ex vivo phrmacodynamic studies of SKI 2053R in beagle dogs to predict the clinical antitumor effect of SKI2053R, comparing with those of cisplatin and carboplatin. In ex vivo pharmacodynamics which used MTT assay as bioassay on the 2 lung and 5 stomach cancer cell, mean antitumor indexes (ATIs) of SKI 2053R were highest among three compounds in both lung and stomach cancer cell lines, especially in stomach cancer cell. Much higher ATI profile and maximal inhibition rates of SKI 2053R appeared in the stomach cancer cells will give desirable advantages to clinical trial s against gastric carcinoma. The anti tumor activity and target organ toxicity of SKI 2053R were compared with those of cisplatin on stomach cancer cell line, KATO III xenografted into nude BALB/c(nu/nu) mice. All groups of cisplatin and SKI 2053R showed active tumor regression. The inhibition rates(IR) of SKI 2053R were higher than that of cisplatin on the basis of mean IR. Though the loss of body weight was observed in all groups from the first week, the SKI 2053R group recovered it soon from the third week after the initiation of treatment, maintaining the most active anti tumor activity among three groups.