Thirty patients with advanced colorectal adenocarcinoma were treated by chemotherapy with an alternating regimen consisting of 5-fluorouracil (5-FU)-mitomycin C and 5-FU-dacarbazine at 3-week intervals. Two patients had a partial response (6%) and 14 a stable disease (47%). The toxicity of this regimen was essentially digestive with 30% of grade 3 or 4 nausea and vomiting. In spite of the reported active and synergistic action of drug association in colorectal carcinoma, this treatment schedule is not better than 5-FU alone. Moreover, gastrointestinal toxicity is increased.