Benzimidazoles carrying the 2-hydroxy-3-(isopropylamino)propoxy side chain at either the C-4 or C-5 ring positions were synthesized and investigated for beta-adrenergic blocking activity. Both compounds demonstrated beta2 selectivity when evaluated in guinea pig atrial and tracheal preparations. The C-4 isomer was 17 times more selective toward tracheal tissue, and its overall potency was roughly comparable to that of propranolol. beta2 selectivity of the C-5 isomer was minimal, with a potency about one-hundredth that of propranolol.