Microwave (MW)-stimulated fixation was applied to surgical pathology and preembedding immunoelectron microscopy. Fresh specimens were microwavedin the fixatives for 15-30sec using a conventional MW oven (500W) containing 200ml of water load. The temperature of fixatives was raised to 35-45°C. After MW radiation, the specimens were kept in the same fixatives for 1-4hr at 4°C or at room temperature as the postfixation procedure, which was important for the completion of chemical fixation of whole specimens. For light microscopical examination, buffered 10% formalin was used. Hematoxylin-eosin staining from paraffin-embedded specimens was completed within 24hr with excellent preservation of morphology and immunoreactivity. For conventional electron microscopy, MW fixation in 2.5% glutaraldehyde-2% paraformaldehyde showed excellent preservation of cell organelles. For immunoelectron microscopy by the preembedding method, 4% paraformaldehyde solution containing 0.1% glutaraldehyde was used, followed by one hr postfixation. Simultaneous improvement of both ultrastructure and antigenicity were obtained without any significant changes of the results. Our results indicate that MW-stimulated fixation with postfixation procedure is a useful tool for various fields of morphological investigations, and its beneficial effects were most remarkable for the preembedding immunoelectron microscopy technique.