Forty-five consecutive patients with advanced colorectal cancer were treated with 5-fluorouracil and high dose folinic acid. Among 43 evaluable patients there were 7 objective responses for an overall response rate of 16%. Toxicity was generally mild and rapidly reversible. Compared to those reported with 5-fluorouracil alone, these results failed to demonstrate an increase in response rate in the treatment of advanced colorectal cancer with the combination of 5-fluorouracil and folinic acid.