Thirty-three patients with advanced colorectal carcinoma were entered on a phase II trial of weekly IV aminothiadiazole (175 mg/m2 escalated to 200 mg/m2) with concomitant allopurinol and non-steroidal anti-inflammatory agents (NSAID's). Toxicity was predominantly GI, cutaneous, and chest pain/dyspnea. Twenty-five percent of patients had grade 3 or 4 toxicity. There were no responses in 27 evaluable patients. Median survival was 12 months. Aminothiadiazole, at higher doses than used in previous reports, when given with NSAID's, had no significant activity against large bowel cancer.