SUMMARY: The urinary excretion of radioactivity after oral administration of 4-14c prednisolone was studied in a patient already receiving large daily doses of non-radioactive prednisolone. The radioactive metabolites in the urine were fractionated by various chromatographic procedures and the following radioactive compounds were identified: prednisolone; prednisone; 11β:17α: 20β:21-tetrahydroxypregna-1:4-dien-3-one; 17α: 20β:21-trihydroxypregna-1:4-diene-3:11-dione; 3α: 11β: 17α:21-tetrahydroxy-5β-pregnan-20-one; 3α: 17α:21-trihydroxy-5β-pregnane-11:20-dione. The significance of these findings is discussed.