Measurement of the concentration of 17-hydroxycorticosteroid (17-OH-CS) glucuronide conjugates in plasma has been suggested as a means of estimating changes in the rate of free steroid metabolism. In the present study a modification of the Nelson-Samuels technique was utilized for the measurement of 17-OH-CS concentration in serum after glucuronidase hydrolysis. This technique proved to be reliable; the results coincided with those obtained by previously reported procedures. The response of the serum free and conjugated 17-OH-CS in normal subjects to maximal adrenal stimulation with corticotropin was compared to the response in patients within seventy-two hours after subtotal gastrectomy. The rise in the serum level of free 17-OH-CS was more rapid following gastrectomy in the surgical patients than following adrenal stimulation in the normal subjects; however, the rise in the serum level of conjugated 17-OH-CS was more gradual in the surgical patients. In view of the variation between subjects, these differences were not statistically significant. In adrenalectomized dogs receiving a constant intravenous infusion of hydrocortisone, laparotomy resulted in a rise in the plasma level of free 17-OH-CS. This manifestation of a delay in steroid metabolism was not correlated with a fall in the plasma level of conjugated 17-OH-CS; the concentration of the conjugates either remained the same or increased. It is concluded that the serum concentration of glucuronide conjugates is determined by multiple factors, only one of which is the rate of their production. As such, their concentration in serum does not reflect the changes in the rate of steroid metabolism that often occur following surgical operations.