This is an important and timely volume. The history of research in homocysteine metabolism can be divided into three periods. The first phase was the exploration of the individual reactions and metabolites that characterize the transmethylation and transsulfuration sequences. The former originated with his description of the biosynthesis of methylpyridine and culminated in the work of Cantoni and Axelrod. Similarly the finding that insulin contained cystine was a potent catalyst for the metabolic and nutritional studies of Rose and du Vigneaud. The description and the definition of...