The synthesis and beta-adrenergic antagonist activities of a group of 1-(heteroaryloxy)- and 1-(heteroaryl)-3-alkylamino-2-propanols is described. beta 1-Adrenolytic (atria) structure-activity correlations indicated that replacement of the 1-naphthyl moiety of propranolol by a 4-quinolyl- (10), 2-quinolyl- (24), or 2-pyrimidyl- (26) heterocyclic moiety resulted in a 10-16 fold reduction in activity. The 1-(4-quinolyloxy)- (10) and 1-(2-quinolyloxy)- (24-25) heteroaryl moieties provided more potent activity than the structurally related 1-[2-(2H-isoquinolin-1-one)]- (31-32) or 1-[3-(3H-quinazolin-4-one)]- (35-36) moieties. All compounds tested exhibited weak beta 2-adrenolytic activity on trachea. Although the most potent beta 1-antagonist, 1-(2-pyrimidyloxy)-3-isopropylamino-2-propanol (26), was 13-fold less potent than metoprolol, it exhibited a beta 1/beta 2 selectivity ratio superior to the cardioselective metoprolol.