Therapeutic effects of 9 antitumor drugs were studied on nude mice inoculated with transplanted human stomach tumor (MKN-28). When cisplatin, cyclophosphamide, chlormethine, 5-fluorouracil or mitomycin C was given ip to nude mice bearing MKN-28 at respective dose of 3, 100, 40, 80 and 2 mg/kg once weekly for 3 wk, the tumor inhibition rates of the former 3 drugs were over 80%, while the later 2 were 70-77%. Cytarabine 200 mg/kg twice or thrice weekly for 3 wk gave an inhibition rate of 68-72%. Hydroxycamptothecin 20 mg/kg twice weekly for 3 wk showed a better therapeutic effect than that given at 40 mg/kg once weekly for 3 wk, the tumor inhibition rates were 65 and 32% respectively. No apparent effect of vincristine and methotrexate on MKN-28 was seen. Histopathological observation indicated that in cisplatin group, numerous necrotic areas of tumor cells as well as sparse infiltration of inflammatory cells were found.