Phenyl[ 1-14C]alanine which is a precursor of the acid moiety of tropane alkaloids and one of the possible intermediates--namely phenylpyruvic, phenyllactic and tropic acids--were simultaneously added to Duboisia leichhardtii root cultures in order to trap the labelled intermediates. When phenyllactic acid was added to 0.5-5 mM, incorporation of phenyl[1-z4C]alanine into the organic acid fraction was much greater in comparison with the cases using phenylpyruvic acid, tropic acid or no intermediate at all. TLC-autoradiogram of the organic acid fraction obtained from phenyllactic acid feeding experiments showed the existence of a radioactive spot corresponding to phenyllactic acid. Trapping of labelled phenyllactic acid was confirmed by recrystallization, NMR and melting point.