A total of 68 patients with non-small-cell lung cancer who either had not previously been treated (38) or had undergone prior therapy (30) were treated in a phase II study of (glycolate-O,O') diammineplatinum(II) (NSC 375 101D; 254-S), a new platinum complex. The drug was given as a single intravenous infusion at a dose of 100 mg/m2 every 4 weeks. All 68 patients could be evaluated for response and 62, for toxicity. Objective responses were seen in 10 of 68 cases (14.7%; 95% confidence interval, 7.3%-25.4%), and the median duration of response was 15 weeks (range, 8-23 weeks). The response rates were similar for previously untreated and treated patients (13% and 17%, respectively), including three previously treated with cisplatin. Myelosuppression was the dose-limiting toxicity. Thrombocytopenia (less than 100,000 platelets/mm3) and leukocytopenia (less than 3,000 WBC/mm3) were observed in 22 (35%) and 18 (29%) patients, respectively. Mild to moderate nausea and vomiting occurred in 45 cases (73%). No significant renal or neurotoxicity was observed. We conclude that as a single agent, 254-S is well tolerated but appears to have marginal activity against non-small-cell lung cancer.