The high pressure liquid chromatographic (HPLC) technique was developed to separate and quantitate the synthetic corticosteroids (s-CS) which are widely used clinically. 1) 12 kinds of s-CS in alcoholic solvent and 2) some of their metabolites in the plasma and urine of healthy subjects with oral administration of s-CS were investigated for the preliminary work. The results are summarized as follows: 1) Cortisol sodium phosphate, Dexamethasone 21, disodium phosphate, Paramethasone acetate, Cortisol acetate, Cortisone acetate, Methylprednisolone acetate, Prednisone, Dexamethasone, 9 alpha-fluorocortisol, Betamethasone, Triamcinolone, and Prednisolone in ethanol were clearly separated by HPLC from Cortisol (F). In the suitable condition of the HPLC (LC-2 type) with a Zorbax SIL column, organic solvent (cyclohexane:dichloromethane:ethanol = 9:4:1)-carrier mobile phases and UV detector, the retention time of each s-CS was obviously different from that of F. The calibration curve was obtained in a linear line with regards to each s-CS. The mean recovery was 97.6% and the coefficient of variation were 1.6 (intraassay) and 7.2 (interassay)%. The sensitivity of the steroid determination was 200pg order. 2) The serial changes in plasma concentrations of s-CS; CS-metabolites and endogenous F were shown in 3 healthy males and 2 females following oral administration of the s-CS. The separated metabolites in number and quality depended on the kind of s-CS. Prednisone and other kinds of the acidified products were separated from prednisolone in the plasma and urinary samples of the healthy subjects as well as Addisonian patients. In conclusion, the HPLC method is useful for the separation and quantitation of the UV-absorbing CS of human plasma and urine. The obtained chromatograms may be an indication of the metabolic state of the subject with treatment of s-CS.