The potential role of atrial natriuretic factor (ANF) in blood pressure (BP) drops during hemodialysis (HD) has been examined in 30 patients with end-stage chronic renal failure. Echocardiographic measurements and evaluation of cardiac parasympathetic function were performed prior to HD sessions, simultaneously with hormonal determinations. The plasma ANF level was correlated with the peak value of the E wave and the Doppler index of the left ventricular preload and was more elevated in ‘denervated’ than in intact patients. During the HD sessions, the BP fell in 18 patients (group 1) and remained stable in 12 others (group 2), despite similar weight losses. Both groups differed by the basal values of plasma ANF, greater in group 1 than in group 2 (100.0 ± 13.3 vs. 65.7 ± 3.4 fmol/ml; p < 0.05). The magnitude of plasma ANF decrease was identical in both groups despite the BP decrease in group 1 at the end of the session. These results suggest that the ANF release depends not only on hemodynamics but also on cardiac innervation in dialyzed patients and that high plasma ANF levels are implied in the BP drops during HD se