Cells obtained from the Nettesheim lung carcinoma of DBA/2 mice, a heterogenous population grown s.c., were cultured as monolayers. These cells were serially subcultured and cloned twice, and a clone was selected for further study. This clone produced malignant tumors at the injected site when injected s.c. into male DBA/2 or C57BL/L x DBA/2 F1 mice. Referred as KLN205, this cell line had the highest rate of lung colony formation on i.v. injection. It was subcultured for over 15 generations, and its cytological characteristics were investigated. The s.c. and lung colony growth were examined histologically. The effects of treatment with two antimetabolite drugs, arabinosyl-6-mercaptopurine (NSC 406021) and 6-selenoguanosine (NSC 137679) were determined in culture and in vivo. The former was relatively ineffective; the latter was very effective both in vivo and in vitro. Several drugs used clinically for the treatment of lung cancer were also tested. This established and characterized cell line is proposed as a potential model for testing other chemotherapeutic treatments.