The aim of the study was to investigate the therapeutic value of reinduction therapy with the same cytostatic treatment that had been used for induction treatment in patients with metastatic colorectal cancer. A total of 71 patients, all of whom had responded or achieved stable disease lasting > or = 12 weeks after six monthly courses of first-line treatment with 5-fluorouracil + racemic leucovorin (5-FU/LV; n = 35) or 5-FU plus the l-isomer of LV (LLV; n = 34) were entered in this study. At the time of relapse, the same treatment was used for initial therapy: racemic LV or LLV was administered at 100 mg m(-2) day(-1) by i.v. bolus injection, immediately followed by 5-FU 400 mg m(-2) day(-1) given as a 2-h infusion. Chemotherapeutic drugs were given on 5 consecutive days at 4-week intervals x 6 or until there was evidence of tumour progression. Among 49 evaluable patients, reinduction therapy that was initiated after a median treatment-free interval of 5.4 months (range 3-14.5) resulted in nine partial response (PR) (18%) and 26 stable disease (SD) (53%), yielding an overall tumour control rate of 69% (95% confidence interval, 54.6-81.7%). The median time to treatment failure from reinduction was 6.4 months, and the median survival duration from reinduction was 8.9 months (20.1 months as judged from the beginning of induction therapy). The toxicity associated with retreatment was generally mild to moderate; compared with initial treatment, there was no significant difference in terms of the overall rate (P = 0.33) or severity (P = 0.19) of adverse reactions. Our data suggest that in patients with advanced colorectal cancer an interrupted treatment strategy, i.e. retreatment with the same regimen in case of relapse > or = 3 months after discontinuation of 6 months of successful treatment with 5-FU/LV or 5-FU/LLV is an acceptable therapeutic concept.