A total of 51 previously untreated patients with non-small-cell lung cancer (NSCLC) were treated with 130 mg/m2 carboplatin given every 4 weeks as an i.v. infusion on days 1, 3, and 5. Ten patients achieved a partial response and five, a minor response. The overall response rate was 20% (95% confidence limits, 8%-32%). The median duration of response was 3 months and the median overall survival was 4.5 months. Leucopenia, thrombocytopenia and anemia of WHO grade 3 occurred in 4%-6% of patients and grade 3 nausea and vomiting was observed in 8% of our subjects. Grade 4 thrombocytopenia occurred in 3 (6%) patients. Apart from nausea and vomiting, nonhematologic toxicities above grade 2 were not observed. Further trials using carboplatin in NSCLC as a single agent or in combination with other chemotherapeutic agents or radiation are warranted.