Alkaloid contents in Argemone mexicana cell line AMMiF were analyzed during a 36-day culture cycle. The benzophenanthridine sanguinarine (SA) represented the main alkaloid. Dihydrosanguinarine(DHSA), a SA biosynthetic precursor and a less toxic benzophenanthridine, was also identified, based on chromatographic properties and further confirmed by gas chromatography coupled to mass spectrom- etry. Along the culture cycle, SA contents increased simultaneously while DHSA decrease, suggesting their biosynthetic conversion. Upon exposure to yeast extract as an inducer of secondary metabolism, there was an increase in SA content, which was preceded by DHS accumulation. However, after a long exposure (72 h), contents of both SA and DHSA were noticeable elevated, with close to 20% of the total alkaloid produced being recovered from the external medium. These results suggest the operation of a cell mechanism to avoid damage inflicted by the excessive accumulation of SA