A cell suspension culture of Papaver somniferum that accumulates small amounts of thebaine was used to investigate the metabolic fate of exogenously supplied (N-14CH3)thebaine. Three metabolites of thebaine still containing the label were discovered and identified as codeine and two new metabolites, tetrahydrothebaine and thebainone. This proves that the poppy cell culture contains the enzymes necessary for enolether cleavage of thebaine at carbon atom 6. Screening of 60 cell suspension cultures of different plant species and of 230 field grown plant species for their capability to metabolize (N-14CH3)thebaine showed that this compound is metabolically inert and only the single cell culture of Mahonia nervosa was capable of cleaving the phenolether methyl group at carbon atom 3 of thebaine to yield oripavine. The field-grown plant of Mahonia nervosa in contrast could not perform this reaction.