Plasma neuropeptide Y-like immunoreactivity (NPY-LI) is elevated in patients with acute myocardial ischaemia and congestive heart failure (CHF) owing to increased activity of the sympathetic nervous system. The prognostic value of plasma NPY-LI with regard to mortality was studied in 324 random patients admitted to a coronary care unit. The one-year mortality was 37% in 113 patients with acute myocardial infarction (AMI) and 18% in those without AMI. Several factors were tested by multiple logistical regression analysis to predict the one-year mortality. Plasma NPY-LI > 60 pmol.l-1, advanced age and previous CHF were independent prognostic factors for an increased risk of mortality in patients without AMI. The mortality rate after one year in non-AMI patients with plasma NPY-LI < or = 60 pmol.l-1 was 14% compared to 69% in those with plasma NPY-LI > 60 pmol.l-1. Increased heart rate was the only independent prognostic factor for increased mortality in AMI patients. Plasma NPY-LI on admission was an independent predictor of mortality in CCU patients without AMI and thus resembles plasma noradrenaline.