In the present study, circadian influences of furosemide on serum electrolytes, lipids and glucose were evaluated in ten hypertensive subjects. A retard capsule (40 mg) of furosemide was given once a day in the morning (07 h 00) or in the evening (19 h 00) for eight weeks. The study was done through a cross-over design. Twenty-four hour urine was collected, and fasting blood samples were obtained during the control period and at the end of each treatment period. The 24-hour urine volume was slightly increased by the repeated administration of furosemide in the morning and evening trials. Urinary excretion of sodium also slightly increased in the morning trial and significantly increased in the evening trial. Serum concentrations of potassium and chloride decreased, while serum uric acid and triglyceride were increased by furosemide treatment. No significant difference was observed in these parameters between morning and evening trials. Fasting blood glucose increased following furosemide. The increment in this parameter was greater in the evening trial than in the morning trial. These findings indicated that the influence of furosemide on glucose tolerance might vary with its time of administration.