Plasma concentrations of atrial natriuretic factor (ANF), catecholamines (adrenaline, noradrenaline, dopamine) and aldosterone, and plasma renin activity (PRA) were measured in a group of 20 patients with moderate to medium heart failure (NYHA class II 7 patients, class III 13 patients), 24 hours after treatment was discontinued. Compared with a control group, plasma concentrations of ANF (p less than 0.01), noradrenaline (p less than 0.05), aldosterone (p less than 0.01) and PRA (p less than 0.01) were significantly increased. There was a significant difference between class II patients and class III patients in plasma ANF (p less than 0.01) and noradrenaline (p less than 0.02) concentrations, but not in PRA and aldosterone levels. A significant correlation was observed between plasma ANF concentration and left ventricular end-diastolic pressure (r = 0.68, p less than 0.001), pulmonary arterial pressure (r = 0.59, p less than 0.01), pulmonary capillary pressure (r = 0.51, p less than 0.02), cardiac index (r = 0.46, p less than 0.05) and left ventricular end-diastolic volume (r = 0.50, p less than 0.05). However, ANF concentration was not correlated with mean right atrial pressure. Plasma adrenaline concentration correlated with systemic arterial resistance (r = 0.80, p less than 0.001), pulmonary arterial pressure (r = 0.57, p less than 0.02), mean pulmonary capillary pressure (r = 0.62, p less than 0.001), cardiac index (r = 0.53, p less than 0.05) and left ventricular end-diastolic pressure (r = 0.58, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)