AbstractIn order to study the pharmacological properties and mode of action of 1‐benzyl‐1‐(3′‐dimethylaminopropoxy)‐cycloheptane fumarate its labelling was performed with14C. The radioactive carbon has been introduced into the benzyl group and into the dimethylamino moiety of the dimethylaminopropoxy side chain. The chemical and radiochemical purity of the two isotopic isomers was proved by thin layer chromatography and auto