After rats were treated with propranolol (50 mg.kg-1, bid, ip) for 7 d, the density of alpha 1-adrenoceptors in the rat myocardial cell membranes increased from 137 +/- 25 to 178 +/- 30 fmol/mg protein determined by receptor radioligand assay. Whereas the KD value was not significantly changed, the relative proportion of alpha 1A-adrenoceptor subtype increased from 19 +/- 6 to 31 +/- 8%. The affinities of two subtypes to 5-methylurapidil were not obviously changed after propranolol treatment. It was suggested that alpha 1A-subtype was more important in alpha 1-receptor mediated alterations after beta-adrenoceptor blockade.