Lutein and zeaxanthin cannot be synthesized de novo in humans, and althoughlutein is abundant in fruit and vegetables, good dietary sources of zeaxanthin arescarce. Certain corn varieties provide adequate amounts because the ratio of endo-sperm b : e lycopene cyclase activity favours the b-carotene ⁄ zeaxanthin branch ofthe carotenoid pathway. We previously described a transgenic corn line expressingthe early enzymes in the pathway (including lycopene b-cyclase) and therefore accu-mulating extraordinary levels of b-carotene. Here, we demonstrate that introgressingthe transgenic mini-pathway into wild-type yellow endosperm varieties gives rise tohybrids in which the b : e ratio is altered additively. Where the b : e ratio in thegenetic background is high, introgression of the mini-pathway allows zeaxanth in production at an unprecedented 56 lg ⁄ g dry weight. This result shows that meta-bolic synergy between endogenous and heterologous pathways can be used toenhance the levels of nutritionally important metabolites.