The present study was carried out to determine, first, the cardiac beta -adrenergic receptor characteristics of normal chickens and chickens with heart failure and, second, the characteristics of myocardial beta -adrenergic receptors in non-hypertrophied hearts in broilers exposed to two different altitude and temperature programmes. The density of beta -adrenergic receptors was significantly lower in myocardial cells in right ventricular failure birds compared with healthy birds. The binding capacity of beta -adrenergic receptors was reduced in the non-hypertrophied ventricles after exposure to high altitude in the younger but not in older chickens. At both altitudes, beta -adrenergic receptor binding capacity was not significantly different in low temperature compared with normal temperature birds. These data support the hypothesis of beta -adrenergic receptor downregulation as one of the mechanisms of cardiac cell adaptation to hypertrophy or hypoxia. Second, the acclimatization to high altitude in older chickens resulted in a normalization of beta -receptor capacity in those broilers that were not affected by right ventricular failure and ascites.