Azosemide is a new monosulfamyl diuretic which inhibits solute transport throughout the thick ascending limb of the loop of Henle. This study compared equal amounts of azosemide and furosemide (20, 40, and 80 mg) in normal subjects. No differences occurred at any dose in volume, sodium, or chloride excretion when analyzed as cumulative excretion at 4, 8, or 12 hr. Azosemide 40 mg caused less potassium excretion than 40 mg of furosemide but there was no significant difference in the sodium/potassium excretion ratio. Analysis of the time course of effect showed that compared to furosemide azosemide tended to have a slower onset of effect. Differences in site of action studies between azosemide and furosemide did not manifest as differences in urinary or electrolyte excretion in our normal subjects.