AbstractSelectively ring‐labelled terodilines (N‐tert‐butyl‐1‐methyl‐3,3‐diphenylpropylamine;1) were prepared by homogeneous catalytic exchange of aromatic hydrogens for3H and2H. In addition, terodilines specifically labelled with14C,3H or2H were prepared from the appropriate 1‐methyl labelled 4,4‐diphenylbutan‐2‐ol, by treating the corresponding tosylates withtert‐butylamine.Emepronium bromide (N‐ethyl‐N,N,1‐trimethyl‐3,3‐diphenylpropylammonium bromide;2) specifically labelled with14C or2H were similarly prepared by treating the labelled tosylates with N‐ethylmethylamine or dimethylamine, followed by quaternization with methyl bro