We have evaluated the effects of dextrofenfluramine treatment on body weight control during a 90 day period, in obese patients on a calorie-restricted diet. The weight loss in dextrofenfluramine-treated patients was significantly higher than in placebo group. The rate of weight loss was linear up to the end of the trial in d-fenfluramine patients. Neural disturbances (vertigo, headache, depression) were the most frequent side effects observed in both the d-fenfluramine and in the placebo-treated groups, without significant differences between the groups. A total number of 23 patients in the dextrofenfluramine group and 20 patients in the placebo group complained side effects. Six patients (five in the d-fenfluramine group and one in the placebo group) discontinued the treatment, due to the side effects. No modifications of the biochemical parameters considered (fasting blood glucose, bilirubin, alkaline phosphatase, creatinine, blood cell counts, asparate-amino transferase (AST), alanine-amino transferase (ALT), total plasma and HDL cholesterol, and triglycerides) were observed at the end of the trial. A significant reduction of total serum cholesterol was observed in both groups at the end of the period of treatment. In conclusion, dextrafenfluramine was proved to be in short term trials an effective and safe tool in overweight control in obese patients.