35S-Furosemide was administered to beagle dogs and rhesus monkeys in an oral solution on a single and a 20 repeated 5-mg/kg/day dosing regimen. Following the single dose, 25.0% (dogs) and 24.0% (monkeys) of the dose were excreted in the urine in 24 hr. TLC analysis demonstrated that both species had similar excretory patterns; i.e., over 80% of the amount excreted in the urine was present as unchanged durosemide and the remainder was composed of a known metabolite, saluamine, and an as yet unidentified metabolite(s). The repetitive dosing regimen did not appear to alter significantly either the total amount recovered in the 24-hr urine or the excretion pattern. Studies in dogs showed that only 50-60% of furosemide was absorbed from oral solution. A significant biliary secretion elimination pathway for furosemide also was observed.