A positive correlation has been previously documented between B-type natriuretic peptide (BNP) levels and left ventricular mass index (LVMI) in hypertensive patients. We evaluated 8 cycling athletes, 8 healthy age-matched controls; 17 hypertensive patients and 7 age-matched controls. LVMI was significantly higher in athletes and hypertensive patients than in their controls. Plasma levels of BNP in hypertensive patients were significantly higher than in athletes and their age-matched controls. No significant difference was found between athletes and their controls. Cycling athletes had significantly larger LVMI than hypertensive patients and controls, without elevated BNP levels. These results suggest that BNP levels are elevated in patients with increased LVM due to hypertension but not in physiologically increased LVM. Whether elevated BNP levels in athletes is a sign of structural heart disease merits further investigation.