The positron emitters carbon-11, nitrogen-13, oxygen-15, and fluorine-18 are receiving ever increasing attention and are being actively utilized in clinical research and application. The advent of the small cyclotron that is easy to operate and maintain and can be readily installed in University Hospitals and the more recent general availability of positron emission transaxial tomographs of sufficient resolution end sensitivity, taken in conjunction with the development of a few radiotracers labeled with positron emitters, have made possible new research and clinical application in neurology, cardiology, and oncology. The use of 11C-labeled palmitate and 18F-labeled 2-deoxy-2-fluoro-D-glucose on a daily basis for studies on stroke, epilepsy, psychiatric disorders, senile dementia, and other pathologic states serve as examples and have readily become routine in a number of institutions. However, these efforts still require a multi-and interdisciplinary approach. The lower doses and possibilities for short-term serial studies are part of the advantage of short half-life radionuclides. Biomolecules of all sorts can be labeled with positron emitters without alteration of their biochemical and physiologic activity. By virtue of the annihilation radiation from the prositron emitter they can be located and quantitated in a small volume element of tissue. Present efforts are focused mainly on measuring metabolic rates in the brain and in the myocardium. Assessing receptor-site action in the brain and heart with labeled neuroleptics is under intensive development. Noninvasive methods that will allow us to evaluate the dynamics of such action in disease states and to quantitate the response to therapy can be expected in the near future. Protein synthesis and cell proliferation rates in measured in vivo are under study. Synthetic techniques and the development of both remotely operated and automated procedures yielding positron emitter labeled biomolecules of all sorts, including simple alcohols, sugars, amino acids, steroids, alkaloids, and a host of drugs, make possible a wholly new area in nuclear medicine. The efforts of the next several years served by increasing interest and investments in this area will demonstrate with positron emitters will be realized.