Twenty-eight patients with inoperable or relapsed lung cancer were given a combination of oral etoposide, administered once a day at doses ranging from 40 to 60 mg/m2/day (d) for 21 consecutive days, and carboplatin, administered intravenously over 1 h at doses ranging from 300 to 400 mg/m2 on day 1 to determine the appropriate doses of this combination. In addition, pharmacokinetic and pharmacodynamic analyses were performed. All the patients had a performance status of 0 to 1. Serum etoposide and free platinum (Pt) concentrations were measured using high-performance liquid chromatography and atomic absorption, respectively. Myelosuppression, nausea and vomiting were the dose-limiting toxicities of this schedule. The maximum tolerated dose (MTD) was 50 mg/m2/d oral etoposide for 21 days and 400 mg/m2 i.v. carboplatin on day 1. For heavily pretreated patients, the MTD was 40 mg/m2/d oral etoposide for 21 days and 350 mg/m2 i.v. carboplatin on day 1. No cumulative increase in the area under the concentration-time curve (AUC) for oral etoposide over time was observed. There were significant correlations between the free Pt serum level (6, 8, 12, 24 h post-dose) and etoposide AUC level (days 1, 10 and 21) for graded hematological toxicity, and the percentage decreases and nadir counts of hemoglobin, leukocytes, neutrophils and platelets. Several pharmacodynamic models were developed to predict the hematological toxicity. In order to facilitate pharmacodynamic evaluations in future studies, a limited sampling model for oral etoposide was also developed and validated.