To investigate the therapeutic value and safety of the biweekly regimen of 5-fluorouracil (5-FU) and leucovorin (LV) plus irinotecan (CPT-11) in patients with previously untreated advanced gastric cancer (AGC). A total of 50 patients (M/F 35/15; median age = 65) with AGC, none of whom had received chemotherapy for advanced disease, were accrued in this trial. Fifteen patients (30%) were 70 years old or older. At the time of their accrual, cytotoxic chemotherapy, consisting of LV 100 mg/m(2) (2-hour i.v. infusion) followed by 5-FU 400 mg/m(2) (bolus) and 5-FU 600 mg/m(2) (22-hour continuous infusion) on therapeutic days 1 and 2 plus CPT-11 180 mg/m(2) (1-hour infusion) on day 1, was initiated. Treatment courses were repeated every 2 weeks until evidence of progressive disease, unacceptable toxicity or withdrawal of consent. All patients were assessable for toxicity and 48 of 50 for response evaluation, having completed at least four courses of chemotherapy. Complete response was achieved in 2 patients (4%, intent to treat) and partial response in 16 (32%) (overall response rate, 36%; 95% confidence interval [CI]: 22%-50%). Twenty-four patients (48%) had stable disease and 6 patients (16%) progressed. The median time to progression was 8 months (95% CI: 6-10 months) and median overall survival 14 months (95% CI: 6-22 months). Between the subgroups of patients <70 years old and 70 or older, there were no significant differences in efficacy. One toxic death occurred. Treatment tolerance was generally mild to moderate and easy to treat. The main grade 3/4 toxicities were neutropenia (32%), diarrhea (16%), and anemia (8%). Grade 3-4 neutropenia was the only treatment-related serious adverse event significantly more common in patients older than those aged <70 (53.3% vs 22.8%, respectively; P = 0.03). Our data suggest that the biweekly regimen of LV and 5-FU plus CPT-11 in untreated patients with AGC is active and has an acceptable safety profile. Further evaluation of this regimen seems to be warranted in a phase III trial.