The opium poppy Papaver somniferum is the commercial source for the analgesics morphine and codeine. Along with these two morphinan alkaloids, opium poppy produces approximately eighty other alkaloids belonging to other tetrahydrobenzylisoquinolin-derived classes. Results from biochemical investigations suggested the involvement of multiple cell types in alkaloid biosynthesis in poppy. In this work, the tissue-specific localization obtained with immunofluorescence microscopy of five enzymes involved in alkaloid biosynthesis is reported: (R,S)-3'-hydroxy-N-methylcoclaurine 4'-O-methyltransferase (4'OMT) central to the biosynthesis of most tetrahydrobenzylisoquinolin-derived alkaloids, the berberine bridge enzyme (BBE) specific to the sanguinarine pathway, (R,S)-reticuline 7-O-methyltransferase (7OMT) specific to laudanosine formation, and salutaridinol 7-O-acetyltransferase (SalAT) and codeinone reductase that lead to morphine. In addition, major latex protein 15 was used as a marker protein for laticifer cells. In capsule and stem 4'OMT , 7OMT and SalAT are found predominantly in parenchyma cells and companion cells of the vascular bundle and COR is localized to laticifers. In developing root tip, 4'OMT, 7OMT and SalAT are found in the pericycle of the stele and the berberine bridge enzyme is localized to parenchyma cells of the root cortex. COR was localized to laticifer cells which occur later in root differentiation. An in situ-hybridisation of the transcripts was performed for the 7omt- and the cor-mRNA. Both transcripts were localized to the companion cells of the vascular bundle of the stem. These results indicate a regulation of biosynthesis by spatial separation of different parts of alkaloid biosynthesis.