Twenty-one patients with metastatic colorectal adenocarcinoma, all previously treated with chemotherapy for metastatic disease, were treated with lonidamine (LDN). The major toxicity encountered was muscular (myalgias in 48%) and gastro-intestinal (nausea and/or vomiting in 52%). Other toxicities included abdominal pain, somnolence, fever, arthralgia and ototoxicity. In the 14 patients evaluable for response we observed no complete or partial remission, 8 stable disease and 6 progressive disease. LND has no clinically worthwhile activity against colorectal carcinoma refractory to conventional chemotherapy.