AbstractL‐dihydroxyphenylalanine‐2H3, L‐tyrosine‐2H2, dopamine‐2H3, 3‐methoxytyramine‐2H3, homovanillic acid‐2H2, homovanillic acid‐2H5and vanillylmandelic acid2H2were prepared by hydrogen‐deuterium exchange under acidic or basic conditions. 4‐hydroxy‐3‐methoxy phenylethyleneglycol‐2H3was prepared from vanillylmandelic acid‐2H by reduction with LiA12H4. The isotopic yield for L‐dihydroxyphenylalanine was 90% and for the other compounds>99%. These labelled compounds could be used as internal standards in the mass fragmentographic analysis of the protium species in tissues and body fluids as well