To assess the relationship between pressor and depressor factors in essential hypertension, the urinary excretion rates of prostaglandins E2 and F2 alpha, kallikrein, vasopressin and aldosterone were compared between 53 untreated hypertensive patients and 53 age- and sex-matched normotensive controls. Mean basal levels of plasma renin activity and of urinary prostaglandins, vasopressin and aldosterone were similar in both groups, but urinary kallikrein was significantly lower in the hypertensive patients. A weak relationship was found in the hypertensives between diastolic blood pressure, and vasopressin or aldosterone, and between vasopressin and prostaglandin E2, and in the normotensives between vasopressin and prostaglandin F2 alpha. In conclusion, these results do not provide evidence for an important imbalance between pressor and depressor factors in essential hypertension, as reflected by the urinary excretion of the major humoral factors and hormones involved in the regulation of blood pressure.