Medical and biological applications of x-rays are reviewed with respect to the application of newly developing x-ray sources, synchrotron radiation, and laser-produced plasma x-rays. Our focus is on the soft x-ray microscopy of biological specimens, including hydrated mammalian cells, and medical applications of hard x-rays such as phase-contrast imaging, high-speed single-shot imaging, and the idea of photon activation therapy. Soft x-ray microscopy with synchrotron radiation has been

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... ly developed in order to make possibleobservations at a resolution of less than 50 nm. However, short single-pulse exposure may be required to image hydrated live biological specimens at high resolution to stop Brownian motion. Laser-produced plasma x-rays are suitable for this purpose. The absorption spectra of biological molecules in the soft x-ray region have been studied in relation to their application to the spectromicroscopy of elements and molecules ina cell. For this purpose synchrotron radiation is the best source. Future study of new modalities of tumor therapy is anticipated.