The effect of the cisplatin analogs carboplatin (CBDCA) or iproplatin (CHIP) was evaluated in patients with extensive non-small cell lung cancer. The randomized phase II design was used to achieve balance between patient groups and comparison of response rates was not a primary objective of the study. CBDCA (400 mg/m2 iv) or CHIP (270 mg/m2 iv) was administered every 4 weeks until relapse of disease. Overall, 11 of 70 patients (16%; 95% confidence interval: 7%-25%) responded to CBDCA and five of 71 patients (7%; 95% confidence interval: 1%-13%) responded to CHIP. There were two complete responses to CHIP and none to CBDCA. The most frequent severe or life-threatening toxic effects were thrombocytopenia and leukopenia. Median survival for patients receiving CBDCA was 6.5 months; for those on CHIP it was 5.0 months (P = 0.59). CBDCA is probably active in patients with non-small cell lung cancer whereas CHIP has limited activity. Further evaluation of CBDCA as part of combination chemotherapy for non-small cell lung cancer is warranted.