A long time has passed since Theophrastus Philippus Aureolus Bombastus von Hohenheim, a reputed German physician and alchemist also known as Paracelsus, wrote in the XV and XVIth centuries that ´´the heart heals the heart, lung heals the lung, spleen heals the spleen... like heals like´´. Physicians have long admitted the possibility of using living tissues as possible therapy for certain type of illnesses. In 1667, Jean-Baptiste Denis attempted what could be considered the first documented cell therapy procedure when he transfused calf´s blood into a mentally ill patient. The German physician Kuettner, a pioneer in live cell therapy, recommended in 1912 that organs should not be transplanted in their entirety but rather cut into small pieces, dissolved in saline solution and injected into the patient. His research was largely ignored. The injection method was all but forgotten until Paul Niehan tried in 1931 to supply parathyroid function in a patient who was too ill to be considered for surgery. Niehan was the first to attempt cell transplantion when he tried supplying parathyroid function by replacing patient glands with those of an ox after the latter had been diced into small pieces in saline solution and injected into the patient. The patient recovered immediately and actually lived for another three decades. Cell therapy involves injection of either whole fetal xenogenic (animal) cells (e.g. from sheep, cows, pigs, and sharks) or cell extracts from human tissue. No one knows exactly how cell therapy works, but proponents claim that injected cells travel to similar organs from which they were taken in order to revitalize and stimulate function and regenerate cellular structure. In other words, cells are organ-specific rather than species-specific. Research furthermore focuses on active therapeutic agents in embryonic and fetal animal tissues distinct from vitamins, minerals, hormones and enzymes. Many. cytokines, growth factors and hormones play major roles in the course of cell division, differentiation, and development. The need for further knowledge and evidence regarding the complexity of these systems awaits further and exhaustive research.