Plasma atrial natriuretic peptide (ANP) levels were measured with a radio-immunoassay in 56 patients, 3 weeks to 16 1/2 years after renal transplantation. At the time of the study their renal function was stable, with creatinine clearances ranging from 10 to 101 ml/min. Plasma ANP levels ranged from 1 to 941 pg/ml and were found to correlate positively with both age and systolic blood pressure. Moreover, a negative correlation was found between plasma ANP levels and creatinine clearance. We conclude that in renal transplant recipients neither renal denervation nor the use of immunosuppressive therapy abolishes the influence of age, systolic blood pressure and renal function on the plasma levels of ANP.