The current use of microwave technology in science creates a dichotomy. Is it the heat or is it the energy? One entire branch of science, chemistry, uses microwave energy to apply heat to a broad range of chemical processes, under pressure, to produce the desired end-products quickly and efficiently (1). The biological sciences, surgical pathology in particular, have tried to adapt the microwave oven to speed up a broad range of processes: fixation, decalcification, antigen retrieval, tissue processing for paraffin and plastic embedding, and histological staining, including special stains, immunolabeling, and in situ hybridization (2). The biologists have assumed that they are also applying heat to speed processing. However, recent improvements in the microwave suggest that the energy is the critical variable (9). We have designed fixation experiments to test the two views.