The concept of stem cell therapy, the repair of damaged or diseased tissue by transplantation of healthy cells, is deceptively simple. This simplicity has led to the hype among desperate patients, their doctors and the media: it would seem that every ailment can be treated with stem cells. At this time, however, the scientific truth is mostly disappointing. The recent claim from Korea of a major breakthrough - the ability to grow stem cells from cloned embryos - turned out to be fraudulent. With the exception ofapplications in haematologic diseases, skin wounds, and bone and cartilage diseases, most of the putative therapeutic applications of stem cell therapy are still under preclinical investigation. These include the treatment of Parkinson's and Alzheimer's disease, paraplegia, cerebral infarction, amyotrophic lateral sclerosis, multiple sclerosis and muscular dystrophy. The treatment of cardiac infarction is currently being investigated in clinical trials.