To evaluate the correlations occurring among plasma atrial natriuretic factor (ANF), renin activity (PRA), aldosterone (ALD) and urinary kallikrein (KK) in young hypertensives and in young normotensives with or without a family history of hypertension, 26 essential hypertensives (mean age: 22.5 +/- 2), 21 normotensives (mean age: 22.3 +/- 1.9) and 13 normotensives with hypertensive heredity (mean age 22 +/- 1.8) under normal Na+ intake (120 mEq/daily) were studied. Blood samples for plasma ANF, PRA and ALD evaluations were taken after a night bed sleep (A) and again after 1 hour of deambulation (B). KK was evaluated on 24 hours urine specimens by the chromogenic substrate (S-2266) method. The results showed that ANF plasma levels in hypertensives (A = 44.5 +/- 19.4 pg/ml, B = 24.1 +/- 11 pg/ml) were higher than in normotensives (A = 38.3 +/- 19.4 pg/ml, B = 19.9 +/- 10.6 pg/ml), with a percentage difference of 13.8% in A situation and 17.4% in B situation. Moreover ANF was higher in normotensives with hypertensive heredity than in normotensives without heredity (A = +7.4%; B = +10%). In B situation ANF was inversely correlated with ALD in all groups (p less than 0.001 in hypertensives; p less than 0.05 in both groups of normotensives), and with PRA in hypertensive group (p less than 0.001). KK was significantly lower in hypertensives than in normals (p less than 0.01) showing only in hypertensive patients an inverse correlation with ANF (r = -0.60; p less than 0.001). In conclusion, our data indicate that raised levels of plasma ANF may be present in young hypertensives with low levels of PRA, ALD and KK.