Even with the standard first-line chemotherapy, advanced non-small cell lung cancer (NSCLC) recurs in most cases. The purpose of this study is to develop a new chemotherapeutic regimen for patients with NSCLC that has relapsed or was refractory to previous chemotherapy. Patients with proven NSCLC refractory or recurrent after previous single-regimen chemotherapy, PS of 0-2, age of 15 years or older, adequate organ functions and measurable lesions were treated with irinotecan at 60 mg/m(2) and cisplatin at 25 mg/m(2) with 1000 ml hydration on day 1. This administration, considered as one cycle, was repeated every week without rest unless encountering defined skip and dose-reduction criteria. The treatment was administered for six cycles over a 49-day period, both median values, to 48 patients, with a response rate of 26%, progression free and median survival times of 3 and 11 months, respectively, and a 1-year survival rate of 46%. The most frequent grade 3 or 4 toxicities were neutropenia, anaemia and nausea, which were manageable. Subset analyses suggested that the response rate was independent of response to the first-line chemotherapy. In conclusion, second-line chemotherapy of weekly irinotecan and cisplatin with minimum hydration seemed effective, with tolerable toxicity, and is potentially useful irrespective of the outcome of previous chemotherapy.