The growth of ultrasound applications in diagnostic medicine has helped stimulate related biological effects investigations. Current data related to effects associated with diagnostic ultrasound indicate the need for additional research on cell surface structures, motility and developmental effects. Research on biological effects, especially for evaluating in vivo end points analogous to those employed by investigators using in vitro systems and simple organisms, are needed. Particular emphasis relative to potential effects on fetal and embroyonic development is indicated. Limited data also suggest the need to investigate possible effects on the immune response. There is a growing realization of the potential importance of nonthermal effects and increasing evidence that the temporal peak intensity is potentially related to the production of some effects. A number of recent comprehensive reviews have helped identify, analyze and evaluate some of the relevant data. Indexing Words: Biological effeds * Safety Medical ultrasound imaging was developed from industrial applications and sonar technology used for the detection of submarines during the Second World War. During the 1950s and 1960s, while ultrasound therapy was becoming an established modality, ultrasound for diagnostic use was primarily in the research stage. The first publications describing the diagnostic application of this new technology appeared in the United States in the early 1950~.l-~ "he first device had an A-Mode display and was a modification of an industrial device. This was followed by the development of a B-mode device capable of producing two dimensional images of tissue structure^.^.^ Growth in the application of this modality and improvement in its image quality has progressed until it has become an important diagnostic tool. This growth stimulated investigations concerning biological From the Office of Science and Technology, National Center for Devices and Radiological Health, Food and Drug Administration, Rockville. MD. Manuscript