The purpose of the program here proposed is to provide training experience in the techniques of nuclear/molecular imaging research as well as a working knowledge of related nuclear medical science to physicians who wish to become researchers in molecular imaging with radioisotopes. Physicians who are trained in these areas will be in the best position to define the future research directions in the field. The proposed program includes formal training in the fundamentals of nuclear medical science, advanced formal training in selected areas defined by the trainee's interests and goals and an extended research experience in the form of a mentored research project, or projects, that will span his/her tenure in the program. The proposed training program will be based in Harvard Medical School's Joint Program in Nuclear Medicine. This program encompasses Nuclear Medicine and related activities in six major Harvard teaching hospitals as well as the University itself. The joint program and its affiliates includes a nuclear medicine residency program as well as several NIH training programs for scientists as well as graduate students thereby giving trainees in the proposed program a large pool of peers with whom to share experience and knowledge. The program faculty consisting of 29 active researchers and practitioners is a unique resource for the training of physician-researchers. These faculty supervise a number of federally funded research programs in which trainees may participate. The training experience is expected to extend over two years. Three positions are requested during the first year with a total of six trainee slots requested during year 2 through year 5. The resources available to the proposed program through the Harvard Medical School Joint Program in Nuclear Medicine are unique in terms of faculty size, extent of research activities and teaching/ mentoring experience of the faculty.