To better understand the biosynthesis of Camptotheca acuminata alkaloids, the effect on camptothecin production of feeding with potential precursors of biosynthesis was studied (i.e., tryptamine and loganin combined. secologanin, and strictosidine). Two key enzymes in alkaloid biosynthesis [i.e., tryptophan decarboxylase (TDC; EC 4.1.1.28) and strictosidine synthase (STR; EC 4.3.3.2)] were also studied. The analyses were conducted using a C. acuminata CG1 cell line that does not produce alkaloids, which could be useful in better understanding the biosynthetic pathway and in identifying possible limiting factors. The activity of TDC was 5 pkat mg-1; the activity of STR was 1.1 pkat mg(-1). Feeding with strictosidine revealed that this precursor is easily biotransformed by two enzymes (i.e., a hydroxylase and a dehydrogenase) in hydroxystrictosidine and didehydrostrictosidine, but camptothecin was never detected. The indole pathway and the low level of STR activity could be limiting factors in the production of camptothecin in the cell line used.