A crossover study was carried out in 22 obese patients to evaluate the effect of a hydrophilic mucilage associated with a 800 calorie hypoglucidic diet, as compared to diet alone, on body weight and on plasma lipid levels. The administration of mucilage resulted in a weight loss greater than that obtained with diet alone. Moreover, plasma cholesterol and triglyceride level reduction was more pronounced in the patients on mucilage treatment. While reduction in plasma triglyceride levels was correlated to variations in body weight, reduction in cholesterol levels was not. This fact may be explained by reduced intestinal absorption of bile acids, as suggested by the significant reduction in plasma bilirubin levels observed in patients on mucilage treatment. During the first period of treatment with mucilage, a slight reduction in plasma levels of iron and calcium was observed, without modifications in red blood cell counts, haematocrit values and haemoglobin concentration. In 6 patients on protracted treatment (6 months), no further modifications in serum iron and calcium levels were observed.