A study of the metabolism of aldosterone in the bullfrog was undertaken to provide a measurable metabolite for the indirect isotope dilution technique for measuring secretory rates. The rate of excretion of labeled aldosterone was considerably slower in the frog than in man and made necessary the collection of excretory products for 5 days to insure reasonably complete recovery of metabolites. The major identifiable metabolite was a tetrahydro derivative subsequently identified as 3β-hydroxy-5β-tetrahydroaldosterone. This metabolite was excreted partly in the free form and partly as a glucuronic acid conjugate. The pH 1-hydrolyzable conjugate of aldosterone was not detected.