To assess the pathophysiological role of renal prostaglandin E (PGE) in renin subgroups of essential hypertension, urinary excretion of PGE before (24 hours urine) and after the administration of furosemide (1 mg/kg, iv) and 2 hours upright posture was estimated in 66 essential hypertensives, classified into high, normal and low renin subgroups. In each renin subgroup, the administration of furosemide and 2 hours upright posture induced marked increases in urinary excretion of PGE and sodium, and in plasma renin activity. However, there were no significant differences in basal values of urinary excretion of PGE among the 3 subgroups, nor in the values after the administration of furosemide and 2 hours upright posture. The present data do not support the hypothesis that the difference in renin level in essential hypertensives is dependent on the synthesis of renal PGE.