Among secondary metabolites, many interesting compounds including flavors, fragrances, and those with pharmaceutical potential can be found. Once the biosynthetic pathway of an interesting compound or group of compounds has been elucidated and the genes encoding the enzymes of the reaction sequence cloned, they can be used for heterologous production in suitable hosts. Combinations of selected genes from organisms which synthesize different end products of a branched pathway makes it possible to design and produce novel products. The potential of this combinatorial biosynthesis has been demonstrated for the synthesis of novel polyketide antibiotics (1 ) and novel carotenoids (2 ).