The present study was designed to investigate the myocardial beta-adrenergic receptor characteristics in T-3-induced ascites in two genetic lines of broilers, in order to look for possible involvement of myocardial beta-adrenergic receptors in the development of broiler ascites syndrome. Myocardial membrane fractions were prepared from 6 and 8 week old chickens fed a 1.5 parts/10(6) T-3 supplemented diet from day 1 in order to increase ascites incidence. Also, a similar assay was performed on myocardial cells of ascites sensitive and ascites resistant chickens at 5 weeks of age. The binding capacity and binding affinity of the myocardial beta-adrenergic receptor of the two genetic lines of birds did not differ significantly, but the tendency of beta-adrenergic receptor binding capacity and affinity constants in ascites-sensitive birds was slightly higher compared to ascites-resistant birds. In commercial broilers, although dietary T-3 significantly increased ascites mortality and the RV/TV ratio compared to control, it did not affect significantly beta-adrenergic receptor characteristics.