A method using high performance liquid chromatography for the quantitative determination of cortisol and 6 beta-hydroxycortisol in urine is described. Urine extracts were fractionated by high performance liquid chromatography. The peak of 6 beta-hydroxycortisol was identified on the basis of retention time (24.4 min) and its area was measured. The peak of cortisol could not be measured simultaneously with the same column because of interference by other absorbing materials. The cortisol and dexamethasone peaks were collected (Rt values 9.6 and 8.1 min, respectively), rechromatographed on another column system, and the concentration was determined. Precision and accuracy of the present method were within the range commonly achieved by other methods established for both steroids. Clinical utility of the present method was evaluated by measuring urinary cortisol and 6 beta-hydroxycortisol in normal subjects, in Cushing's syndrome and disease patients, and in patients receiving cortisol therapy.