AbstractTwo cardioselective beta‐adrenoceptor antagonists: dl‐acetanalide‐4′‐[3‐(isopropylamino)‐2‐hydroxypropoxy] (“practolol”), and dl‐chloroacetanilide‐4′‐[3‐(isopropylamino) ‐2‐hydroxypropoxy](“chloropractolol”), labeled with tritium at positions 3′ and 5′of the aromatic ring were prepared. The starting 3 materials for the synthesis of the aryloxypropanolamines was 2,6‐di‐3H‐4‐acetamido phenol, prepared by catalytic dehalogenation of 2,6‐dibromo‐4‐acetamido‐phenol, employing tritium gas. Condensation of 2,6‐di‐3H‐4‐acetamido‐phenol with epichlorohydrin, followed by epoxide ring opening with isopropylamine yielded 3′ 5′‐di‐3H‐acetanilide‐4′‐[3‐(isopropylamino)‐2‐hydroxypropoxy], (3′,5′‐di‐3H‐ practolol). Deacetylation of 3′,5′‐di‐3H‐practolol followed by selective ar‐N chloroacetylation of the resulting 1‐(2′,6′‐di‐3