The isolation of 18-hydroxycortisol from the urine of patients with primary aldosteronism was recently described and no synthetic procedure was available for its preparation. The C-13 angular methyl group of prednisolone-17 alpha,21-acetonide-11 beta-nitrite was functionalized by photolysis in the presence of oxygen to give the product 18-hydroxy-prednisolone-17 alpha,21-acetonide-18-nitrate. The 18-nitrate was reduced with zinc and ammonium acetate to the corresponding 18-hydroxy compound, 18-hydroxy-prednisolone-17 alpha,21-acetonide. Homogeneous hydrogenation with Tris(triphenyl-phosphine)rhodium (I) chloride as catalyst resulted in the formation of 18-hydroxy-cortisol-17 alpha,21-acetonide. Acid hydrolysis of the latter compound gave 18-hydroxycortisol. Oxidation of 18-hydroxycortisol-17 alpha,21-acetonide with pyridinium dichromate followed by acid hydrolysis gave 18-hydroxycortisone. The 18-hydroxylated steroids exist as the 18,21-hemiacetals. Catalytic reduction with tritium gas with Tris(triphenyl-phosphine)rhodium (I) chloride of 18-hydroxyprednisolone-17 alpha,21-acetonide and acid hydrolysis gave [1,2(3)H]18-hydroxycortisol.