In order to determine the relationships between allograft function and the recipient's plasma concentrations of atrial natriuretic factor (ANF), plasma ANF was measured by radioimmunoassay for 14 days after cadaveric renal transplantation in 9 patients aged 19–64 years. All received immunosuppression with prednisolone, azathioprine, and cyclosporine. No patient was in heart failure. During the study period, six grafts functioned, and three were nonfunctioning—two due to rejection and one to acute tubular necrosis.Plasma ANF concentration at the time of transplantation was 48±16 pmol/L (mean ± SEM) range 15–145 pmol/L. In the six patients with functioning grafts, ANF declined in parallel with the fall in serum creatinine (658±35 to 210±34 μmol/L). In the three with nonfunctioning grafts, serum creatinine and plasma ANF concentration both increased. There was overall a significant linear relation between serum creatinine and plasma ANF (r=0.527,P< 0.001). The changes in