Incorporation studies of the known heimia alkaloid precursors [3H]lysine/[14C]phenylalanine into the three types of alkaloids, phenylquinolizidinols, phenylquinolizidinyl p-coumarates and biphenylquinolizidine lactones, produced by in vitro-grown Heimia salicifolia indicate that whereas within an alkaloid type both the cis-fused and trans-fused alkaloids originate from a common metabolic pool, the three types of alkaloids are formed from different precursor pools. The data suggest that the biphenylquinolizidine lactones are derived from neither the phenylquinolizidinols nor the ester alkaloids that accumulate in the cultures. Studies with [3H]lysine/[14C]p-coumaric acid confirm these findings and further indicate that p-coumaric acid is a precursor to both the phenylquinolizidinyl- and the p-coumaroyl group of the alkaloids. © 1994.