Lonidamine was studied in advanced cancer patients. The drug was given orally by single or repeated administrations. Single doses ranged from 150 to 450 mg. Repeated administrations were performed with progressively increasing doses: 450–900 mg daily. Lonidamine lacked severe toxic effects after both single and prolonged administrations. The most common side effect was myalgia; gastrointestinal discomfort was also reported. 1 patient with lung cancer experienced an episode of arrhythmia which subsided upon discontinuation of treatment and did not reoccur when treatment was reinstated. 1 partial and 2 minor responses were observed in the 6 patients with breast cancer.