The effects of low bolus dose (70 +/- 6 micrograms [mean +/- SEM]) atrial natriuretic factor (ANF) administration was assessed in 16 patients with chronic congestive heart failure. Measurements were made for at least 60 minutes before and after the dose of ANF. There was a significant increase in urine flow rate (0.81 +/- 0.06 to 1.81 +/- 0.23 ml/min, p less than 0.01), sodium excretion rate (56 +/- 14 to 80 +/- 23 microEq/min, p less than 0.01), fractional excretion of sodium (1.23 +/- 0.49 to 1.63 +/- 0.60 percent, p less than 0.01) and potassium excretion rate (35 +/- 7 to 42 +/- 6 microEq/min, p less than 0.02). However, no significant alterations in renal plasma flow or glomerular filtration rate were observed. Furthermore, there was no significant correlation between the change in urine flow rate or sodium excretion rate and the change in renal plasma flow or glomerular filtration rate, respectively. In addition, there was no significant effect on cardiac index, mean aortic or left ventricular filling pressures, or systemic vascular resistance. There also was no discernible relationship between the response to ANF and the baseline concentrations of plasma ANF, aldosterone, or plasma renin activity. Thus, in patients with congestive heart failure, low dose ANF boluses may produce an increase in urine flow rate and sodium excretion rate that is independent of renal plasma flow or glomerular filtration rate. This suggests a meaningful direct renal tubular effect of exogenous ANF in this setting.