We have directly compared atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), and N-terminal pro-ANP (N-ANP) as markers of patients with left ventricular ejection fraction (LVEF) <or = 35%, as measured by radionuclide ventriculography. Venous blood samples were obtained from an unselected group of 87 patients who had been referred for assessment of ventricular function. ANP, BNP, and N-ANP were measured by radioimmunoassay using commercial kits. Receiver-operating characteristic analysis was used for the objective assessment of the diagnostic performance of each assay. There was a weak negative correlation between LVEF and plasma levels of ANP-li (r = -0.50,), BNP-li (r = -0.57), and N-ANP-li (r = -0.49) (p 4 pmol/L-sensitivity 1.0, specificity 0.58; N-ANP >200 pmol/L-sensitivity 0.95, specificity 0.35; and ANP >10 pmol/L-sensitivity 0.90, specificity 0.30. Plasma concentrations of BNP and N-ANP provide sensitive indicators of moderate to severe LV dysfunction; both peptides, are objectively superior to ANP for identifying patients with LVEF <or = 35%. These simple tests could be used to screen patients with suspected ventricular dysfunction to reduce the demand for further cardiac investigations.