In two large controlled cooperative trials, 1118 patients undergoing surgical resection for large bowel cancer were randomized to be treated by surgery alone or to receive 5-fluorouracil during postoperative followup. The two studies differed slightly in the selection of patients for entry and in the dose regimens of 5-fluorouracil. Following examination of the removed specimen, "curative" and palliative stratifications based on evidence of residual disease were made, so that the two trials actually consisted of five separate patient groups, two groups of patients who had "curative" resections and the other three smaller groups of patients who had palliative resections with residual disease or tumor at a margin of the resected specimen. In all five groups, survival was slightly better in patients receiving chemotherapy although no single difference is statistically significant. Any suggestion that these slight advantages represent a true therapeutic 5-FU effect must be tempered by previous negative adjuvant studies by this group as well as others. Currently the group is conducting a trial using a combination of methyl-CCNU and 5-fluorouracil and has recently added a nonspecific immunostimulant, methanol extraction residue of BCG (MER), to one subgroup.