It is reported that the combination of cisplatin (CDDP) and carboplatin (CBDCA) is synergistic in vitro. The objective of this study was to evaluate the therapeutic effect and safety of the two platinum compounds in combination with etoposide in the treatment of non-small-cell lung cancer (NSLC). Forty patients were registered. Based on the results of a phase I study, patients were treated with CDDP (80 mg/m2 i.v. on day 1), CBDCA (280 mg/m2 i.v. on day 1), and etoposide (80 mg/m2 i.v. on days 1-3). Of the 40 patients, 30 were men and 10 women. Histology revealed adenocarcinoma(AC) (n = 20), squamous cell carcinoma(SCC) (n = 18), and large cell carcinoma(LCC) (n = 2). Staging: IIIA (n = 3); IIIB (n = 17); and IV (n = 20). A 32.5% overall response rate [13 of 40; 95% confidence interval (CI) 18-47%] was achieved. The response rates in patients with SCC and AC were 55.6 and 10.0% (p < 0.005), respectively. The median duration of response was 47.1 weeks and the overall median survival time was 57.1 weeks. Leukopenia and thrombocytopenia--World Health Organization (WHO) grade IV--occurred in nine and 11 patients, respectively. Nonhematological toxicities were mainly nausea, vomiting, and alopecia. In conclusion, further investigations of this regimen are warranted in the treatment of NSLC.