The origin of most medical problems is biochemical in nature. Positron emission tomography (PET) is a powerful tool to enlighten the underlying biochemical disorder in human disease. Therefore, the biochemical information obtained by PET allows an understanding of the fundamental nature of human disease and provides diagnosting examinations with a high sensitivity coupled with a high specificity. Moreover PET can assist in the selection and monitoring of therapeutic correction. Initially PET was available only for research rather than clinical practice since it was an expensive and complex technology that necessitated an on-site cyclotron. However, the current trend shows a transition from research to clinical practice as a result of development of new radiopharmaceuticals, improving technology, commercially available "baby" cyclotrons and generator-produced radionuclides and automated radiochemistry systems. Already there are three established clinical applications: detecting coronary artery disease and myocardial viability, lateralizing the seizure focus in focal epilepsy and the diagnosis/localization as well as grading of brain tumors. Academic and commercial programs are being carried out in over 80 academic PET research centers and over 20 commercial companies all over the world. Academic programs are developing new radiopharmaceuticals, new procedures and new uses of PET. In the mean time academic and commercial programs are trying to lower the complexity and cost of the clinical applications of the technology. Recently the best resolution so far was achieved by the designers of the Donner-600 crystal PET scanner, the intrinsic resolution being 2.6 mm. Another major development was a new computer software system that enabled combined display of PET and three-dimensional brain magnetic resonance (MR) image, Therefore, it will be possible to correlate on the same video screen PET images with other imaging modalities such as CT and MR. This will enable to integrate biochemical/physiologic information with complementary anatomic data. Taking into account the enormous scope in diagnostic imaging, clinical research and consequent clinical applications PET has the potential to be the modality of choice in functional imaging. It seems that it is time for Turkey to plan her policy regarding when and how to start thissophisticated and expensive imaging modality that has opened new frontiers in medical imaging.