AbstractNorepinephrine‐d10, d11deuteriochloride anderythro‐α‐methylnorepinephrine‐d6, d7hydrochloride for use as mass spectrometric stable isotope internal standards have been synthesized. Trideuteriomethylation of the lithio derivative of 3,4‐dimethoxyacetophenone provided the corresponding 1‐(3,4‐dimethoxyphenyl)‐1‐propanone‐3,3,3‐d3. Bromination followed by treatment of the resulting α‐bromoketone with dibenzylamine yielded the α‐dibenzylamino derivative of 1‐(3,4‐dimethoxyphenyl)‐1‐propanone‐3,3,3‐d3. Deuterium bromide cleaved the methyl ether groups and introduced three to four additional deuterium atoms in the resulting catechol. Catalytic hydrogenation gave the desirederythro‐α‐methynorepinephri