Twenty-one patients with inoperable colon cancer in the pelvis were treated with intra-arterial 5-fluorouracil (5-FU) and mitomycin C, given bilaterally into the internal iliac arteries. Seventeen of the 21 patients had failed previous radiation therapy and 15 had also failed systemic intravenous chemotherapy. Eighteen of the 21 patients received intra-arterial treatments because of pelvic pain. Effect of this treatment on the pain could be evaluated in 16 patients. A measurable decrease in pain medication occurred in 8 of 16, whereas a subjective feeling of pain relief was observed in 12 of 16 patients for a mean period of 3.5 months. However, objective tumor response was considered definite only if associated with a greater than 50% decline of an elevated plasma carcinoembryonic antigen level; this was observed in 5 of 11 patients (45%). Reduction in tumor mass as measured by imaging techniques was observed in two of ten patients in whom it was evaluable. Improvement in hydronephrosis was observed in five of seven evaluable patients. Hematuria was present in 12 patients and improved in 10 of those patients. The most significant side effect of chemotherapy was perineal and gluteal skin erythema, which was observed in 36% of the patients after the first course and in 24% during the second course. This frequently escalated to cutaneous vesiculation and desquamation. This side effect was prevented by concurrent administration of steroids. Pelvic arterial infusion of 5-FU and mitomycin C can offer temporary pain relief to patients who have failed other means of therapy. Objective antitumor effects may have also resulted but were much harder to assess in this group of patients.