Background: Lobaplatin, D-19466, 1,2-diaminomethyl cyclo-butane ρlatinum(II)lactate, is a new, water-soluble platinum complex which we expected would have a better therapeutic index than either cisplatin or carboplatin, since various murine and human tumor models had previously indicated effectiveness. Furthermore, a phase I study demonstrated that Lobaplatin was successful in the treatment of bronchogenic carcinomas. Patients and Methods: A total of 39 patients with inoperable advanced non-small-cell lung cancer (NSCLC), previously untreated by chemotherapy or radiotherapy, were included to receive Lobaplatin in a dose of 50 mg/m2 once every 4 weeks as a single bolus injection. Results: Of the 39 patients included, 33 were evaluable for response according to protocol. There were no complete remissions, and only 1 patient (3%) had a partial response. Most of the patients showed no change (54.5%), with the time to progression ranging between 8 and 28+ weeks. The data of 38 patients were used for the toxicity analysis. Nausea and vomiting were the leading clinical problems in nonhematological toxicity and appeared in 27 (71%) patients (in 18% of patients with WHO grade III). Regarding hematological toxicity, the leading problem was thrombocytopenia, with WHO grades III and IV in 6 and 5 patients, respectively. Conclusion: Lobaplatin was well tolerated when applied as a 50 mg/m2 single bolus intravenously in 4-week intervals. However, regarding its effectiveness, our phase II study found it to be only marginally effective in the dose and schedule used. Therefore, our results provide no support for further use of this treatment plan in patients with NSCLC