ABSTRACT. Forty moderately overweight men with high waist/hip girth ratio and mild hypertension participated in a trial with gel-forming fiber—guar gum. After two weeks of familiarization and controlled food intake, ensuring weight stability, the participants received 7 g of guar three times daily during two weeks. Patients were then followed during a 5-week wash-out period. There were no changes in body weight and body composition but total cholesterol decreased during gum treatment. Blood pressure measured at standing, supine and sitting positions decreased after two weeks of guar treatment by 9.8% systolic and 9% diastolic and did not revert to pre-treatment values until after three weeks of the wash-out period. There was also a decrease in both systolic (8 %) and diastolic (7%) blood pressures during exercise on the ergometer bicycle at 50 and 100 W (4.6 and 4.7% respectively) submaximal work load. It is concluded that mar gum exerts a lowering effect on the blood pressure in moderately obese men even in the absence of any change in body weight. If confirmed in further long-term studies, guar may be a valuable alternative to pharmacological preparations in the treatment of mild hypertension.