The isolation of 18-hydroxycortisol and 18-oxocortisol was recently described. These steroids have been shown to be excreted in exaggerated quantities in patients with primary aldosteronism, with adrenal adenomas and in glucocorticoid suppressible aldosteronism. We report the measurement of both steroids in the urine of patients with essential hypertension. 18-Oxocortisol excretion did not differ in patients with normal renin essential hypertension (0.7 +/- 0.7 micrograms/24 h), low renin essential hypertension (0.7 +/- 0.5 micrograms/24 h) and normal individuals (1.2 +/- 0.9 micrograms/24 h). Patients with normal renin hypertension excreted 54 +/- 43 micrograms/24 h of 18-hydroxycortisol, those with low renin essential hypertension excreted 58 +/- 54 micrograms/24 h, and normal individuals excreted 63 +/- 36 micrograms/24 h. Three of the low renin and one of the normal renin hypertensive subjects excreted greater quantities of 18-hydroxycortisol than the upper limit of normal, but all excreted normal quantities of 18-oxocortisol. As 18-hydroxycortisol is inactive, the meaning of this elevated excretion is unclear, but it may be a marker of an adrenal enzymatic abnormality which may be playing a more direct role in hypertension.