To investigate the variability and the mechanism of negative T waves in hypertrophic cardiomyopathy (HCM), especially giant negative T waves in apical hypertrophy, from view point of adrenergic function, ECG was studied by treadmill exercise test and under administrations of beta-adrenergic agonist (isoproterenol) and antagonist (propranolol) in 33 patients with HCM and negative T waves. Apical hypertrophy was seen in 16 cases, and giant negative T waves were seen in 24 cases. By treadmill exercise test, negative T waves became less deep in all cases of HCM (-1.2 +/- 0.5 mV-----0.6 +/- 0.5 mV, p less than 0.001). The higher exercise level the patients attained, the less deep the negative T waves became. Isoproterenol caused the same reversal of negative T waves as the exercise test, but heart rate and rate pressure product attained by isoproterenol were significantly smaller than those by exercise. R wave amplitude did not change with isoproterenol. Propranolol made negative T waves deeper at rest and inhibited the reversal of negative T waves caused by exercise. In conclusion, negative T wave in HCM, especially giant negative T wave in apical hypertrophy, is variable. Beta-adrenergic function may be at least one of its mechanisms.