The objective of this study was to assess the efficacy and safety of two regimens of irinotecan, combined or alternated with bolus 5-fluorouracil (5-FU) and folinic acid (FA), and the Mayo Clinic regimen as first-line therapy for colorectal cancer (CRC). A total of 152 patients with advanced CRC were randomised, and 149 patients were treated intravenously by irinotecan 125 mg/m2, FA 20 mg/m2 followed by 5-FU 500 mg/m2 bolus, weekly for 4 weeks (arm A, Saltz regimen; n=46), or irinotecan 350 mg/m2 alternating with FA 20 mg/m2/day followed by 5-FU bolus 425 mg/m2/day for 5 days (arm B; n=53), or FA 20 mg/m2/ day followed by 5-FU bolus 425 mg/m2/day over 5 days every 4 weeks (arm C, Mayo Clinic regimen; n=50). Patients were analyzed for tumor response, time to progression, overall survival, safety and quality of life. The overall response rate for evaluable patients in arm A was 33% [95% confidence interval (CI), 17-49%], in arm B was 32% (95% CI, 16-49%) and in arm C was 26% (95% CI, 12-40%). Median times to progression were 7.9, 7.0 and 6.9 months and median survival times were 22.2, 17.0 and 18.2 months for arms A, B and C, respectively, in the intention-to-treat population. The main grade 3-4 adverse events were neutropenia (7%, 39% and 12%) and diarrhea (6%, 21% and 18%). In conclusion, both regimens containing irinotecan were active and well tolerated in patients with advanced CRC.