Threo- and erythro-2-(alpha-hydroxybenzyl)-3,3-dimethylaziridines (1a and 1b) and threo-2-[alpha-hydroxy(2-naphthyl)methyl]- and 2-[alpha-hydroxy(3,4-dichlorobenzyl)]-3,3-dimethylaziridines (1d and 1c) have been prepared as conformationally restricted analogues of beta-adrenoceptor blocking agents like dichloroisoproterenol (DCI) and pronethalol. The aziridine analogues 1 except possibly 1c are competitive antagonists of isoproterenol-induced response on a guinea pig tracheal chain preparation and the order of potency is 1d greater than 1a greater than or equal to 1b greater than propranolol greater than 1c. Unlike propranolol, these compounds have no effect on the isoproterenol-induced response on guinea pig auricles and no significant local anesthetic and antiarrhythmic activity. The aziridine analogues 1 represent the first of a new class of selective beta2-adrenoceptor blocking agents.