Fifty urological patients with normal renal function, or with either chronic or acute renal failure were treated with Bumetanide infused in saline or a 5% glucose or fructose solution. Thirty-two patients were given Bumetanide exclusively, whereas 18 were given alternating infusions of Bumetanide and Furosemide. During Bumetanide administration a statistically significant increase of urinary Na+ and H2O excretion and decrease of serum urea and creatinine occurred. As Furosemide and Bumetanide behaved clinically in the same way during identical trial conditions, it is possible that these diuretics may have the same mechanism of action. However, when infused, as in our trial, Bumetanide is much more potent on a weight for weight basis than Furosemide. Apart from the expected loss of potassium, no side effects were recorded during Bumetanide medication in this study.