During the last 10-12 years, the research on homocysteine has become very active. About 1500 of articles are now published each year on homocysteine and the vitamins involved in its metabolism. A disturbed homocysteine metabolism can be an underlying factor for pregnancy complications and fetal malformations, cardiovascular disease, dementia, psychiatric and neurologic disorders and possibly carcinogenesis. A disturbed homocysteine metabolism can in most cases be normalised by treatment with folate and/or vitamines B12 and B6. Many of these findings therefore directly concern most practitioners. However, if there are good reviews covering single aspects of this research, these are published in specialised journals. The author has realised the difficulties for the practitioner in keeping updated. This second edition has been thoroughly updated and also offers more data on the vitamins. Over 1600 references are made available.