1. The 24 h urinary excretions of Porter—Silber (P—S) chromogens, 17-hydroxycorticosteroids (17-OHCS) and free cortisol, and day-night variation of plasma P—S chromogens, were studied in normal and obese women and patients with a confirmed diagnosis of Cushing's syndrome.
2. The mean absolute values of P—S chromogens, 17-OHCS and free cortisol were similar for the normal and obese subjects and elevated in Cushing's syndrome. With the exception of the 17-OHCS there was some overlapping of the individual values within the three groups. All the subjects with Cushing's syndrome and several of the obese subjects had values of 17-OHCS which were outside the normal range.
3. The 24 h urinary 17-OHCS and free cortisol excretion expressed per kg body weight were significantly lower for the obese than for the control subjects and subjects with Cushing's syndrome. The values were significantly higher for the subjects with Cushing's syndrome than for the obese and normal subjects. There was some overlapping of the individual values.
4. Two normal and two obese subjects failed to show significant day-night variation, whereas only four of the patients with Cushing's syndrome had significant day-night variation of plasma P—S chromogens.
5. The urinary 17-OHCS for four of the obese subjects with some symptoms of adrenocortical hyperactivity were suppressed normally on a low dose of dexamethasone whereas those with Cushing's syndrome failed to do so.