The course of alkaloid accumulation and laticifer cell appearance was compared in germinating P. bracteatum seedlings. Seedlings of various ages (0-14 days old) were analyzed for their dopamine, thebaine, morphinan alkaloid immunoreactivity, and benzophenanthridine alkaloid levels. Simultaneous electron microscopic studies revealed that seedlings were devoid of laticifer initials until day 3, where-upon their numbers increased with time. The appearance of appreciable amounts of thebaine only occurred after day 4 of germination. Conversely, dopamine was rapidly formed at the onset of germination and reached millimolar concentrations well before laticifer cells were detected. Benzophenanthridine alkaloid levels remained fairly constant over the period analyzed. These results support the theory that the presence of laticifer cells is necessary for the accumulation of morphinan but neither benzophenanthridine alkaloids nor their mutual precursor, dopamine.