The first patient to respond to [(glycolato-0,0') diammineplatinum (II)] (254-S) in a clinical phase I study is reported. The patient was a 52-year-old man complaining of nausea and weight loss. A chest X-ray demonstrated a diffuse infiltrating shadow in the right lung. A transbronchoscopic brushing of the right upper lobe and a biopsy specimen from the right supraclavicular lymph node revealed adenocarcinoma of the lung. He was diagnosed as having primary lung cancer with distant lymph node metastasis. 254-S was administered by intravenous drip infusion to a dose of 100 mg/m2. Two weeks after the second 254-S treatment, a chest X-ray demonstrated a more than 50% reduction in the pulmonary shadow and met the WHO criteria for a partial response. Thrombocytopenia, leukocytopenia and moderate nausea were observed as adverse effects of 254-S but renal toxicity was not found. Pharmacokinetics of free platinum in this patient demonstrated biphasic decay with a peak plasma concentration of 8.09 micrograms/ml. A disease-oriented phase II study of 254-S against non-small cell lung cancer should be performed to establish the efficacy of this new platinum complex.