All randomized controlled trials of adjuvant therapy of colorectal cancer, published up to December 1986 in English, were reviewed. Eight trials compared radiotherapy groups with control groups in rectal cancer (3062 patients), and 17 trials compared chemotherapy groups with control groups in colorectal cancer (6791 patients). The results of trials testing radiotherapy or chemotherapy were combined. Fluorouracil-containing regimens resulted in a small benefit of therapy in terms of overall survival, with a mortality odds ratio of 0.83 in favor of therapy (95% confidence interval, 0.70 to 0.98). All other combinations of trials failed to show statistically significant differences between treated and control patients, even though the odds of death tended to be slightly lower in treated patients, especially those with rectal tumors. Some overall survival benefit from adjuvant therapy cannot be excluded, but it is likely small. Such small benefit, if real, would be far from negligible in a common case of malignancy with long survival expectancy. Trials much larger than those published up to now are needed.