During the last 8-10 years the research on homocysteine has become very active. Hundreds of articles are now published each year. 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 normalized by treatment with folate and/or vitamines B12 and B6. Many of these findings therefore directly concern most practitioners.