We have measured the urinary cortisol production rate (uCPR) simultaneously with the serum cortisol production rate (sCPR) in four healthy men within a period of 3 days. uCPR, determined by isotope dilution of 11-oxoetiocholanolone was compared with sCPR, which was measured in three different ways (a, b, c). Blood was sampled at 10-min intervals for 24 h, and deconvolution analysis was applied to the cortisol concentrations. The daily serum cortisol production per liter, multiplied by the distribution volume yielded sCPR. The measurement methods are characterized as follows: a) the secretion and elimination terms were free; b) like method a, but with the input of the rate constants alpha and beta into the elimination function; c) the average 24-h cortisol concentration was multiplied by the metabolic clearance rate. uCPR was 25.4 +/- 4.7 [range: 21.3-31.4] micromol/(m2 x day), sCPR (method a) was 28.8 +/- 4.5 [range: 23.5-34.3] micromol/(m2 x day), sCPR (method b) was 27.9 +/- 8.1 [range: 18.5-37.7] micromol/(m2 x day), and sCPR (method c) was 29.3 +/- 4.8 [range: 22.7-33.2] micromol/(m2 x day). uCPR did not significantly differ from each of the 3 sCPR values (P > 0.30; > 0.46; and > 0.06, respectively). The patterns of the cortisol secretory rates in the present and previous studies do not necessarily represent the physiological process of the secretory bursts. We conclude that the estimated CPR, being 25-30 micromol/(m2 x day) [9-11 mg/(m2 x day)], can serve as a guideline for glucocorticoid replacement dose and that the urinary route to measure CPR is preferred because of its relative ease.