Concerned with discovering the chemical pathways of biosynthesis, this book devotes four chapters to the use of isotopes in biosynthetic research and the biosynthesis of enzyme cofactors and vitamin B12 and of reduced polyketides such as erythromycin. The topics covered demonstrate the revolution that has occurred in biosynthetic studies with the advent of gene cloning and overexpression. Yet the book also shows that the more classical approach to biosynthetic studies must go hand in hand with these new techniques.