A prospectively designed phase II study of non-small cell lung cancer stage IIIb and IV treated by gemcitabine and cisplatin was studied. The dosage of gemcitabine was 1 g/m2 weekly on day 1, 8 and 15. Cisplatin 100 mg/m2 was given on day 15 of each 28 day cycle. Twenty-eight patients were treated and all cases were evaluated for response. Survival and toxicity were determined in all enrolled patients. Thirteen (46.4%) achieved partial response (PR). By using Kaplan Meier's method the mean survival time was 19.8 months. One year survival was 66.6 per cent. Non hematologic toxicity consisted of mild nausea, vomiting, alopecia and hyperpigmentation of the skin. Rising creatinine of grade I was seen in 1.6 per cent. Anemia and leukopenia were common hematologic side effects with 27.5 per cent and 14.2 per cent of patients experiencing grade III and IV toxicity respectively. Both side effects were usually short lived and responsible for the delay of gemcitabine administration on day 8 and 15 in 18.3 per cent and 23.3 per cent on day 15 alone of chemotherapeutic courses respectively. We conclude that the combination of gemcitabine and cisplatin at this dosage achieved good response with moderate side effects.