A series of binary (aryloxy)propanolamines has been prepared and examined in vitro and in vivo for beta-adrenoreceptor blocking activity. These symmetrical compounds consist of two (S)-(phenyloxy)propanolamine pharmacophores coupled through alkylenedioxy or poly(oxyethylenedioxy) linking units of varying lengths. Examples of such binary compounds linked through the 2,2', 3,3', and 4,4' positions in the aromatic rings of the pharmacophores have been prepared. In vitro and in vivo test data indicate that the 2,2' compounds tend to be selective beta 2-adrenergic blocking agents, the 4,4' binaries tend to be selective beta 1-blocking agents, and those compounds with 3,3' linkages exhibit intermediate selectivities. One of the 4,4'-linked binary compounds, 4s, exhibited potent, cardioselective beta-blockade in vivo, which was of short duration and was accompanied by a prolonged tachycardia.