SUMMARY: The metabolism of [3H]betamethasone has been studied in normal subjects and in patients receiving high therapeutic doses of the steroid. About 70% of the dose was excreted in the urine in 48 hr.; 15–30% of the dose was found in the unconjugated fraction. Six metabolites as well as unchanged betamethasone were isolated and identified by paper chromatography using reference compounds prepared from [3H]betamethasone. The transformations were: oxidation of the 11β-hydroxyl group, hydroxylation at the 6β-position, reduction of the carbonyl group at C-20 and removal of the side chain to give 17-oxosteroids.