Endospores from Bacillus megaterium NCIMB 7581, B. stearothermophilus NCIMB 8922, Clostridium sporogenes NCIMB 8053 and Thermoanaerobacterium thermosaccharolyticum NCIMB 9385 were subjected to varying regimes of microwave radiation under controlled conditions. The effects of this form of thermal excitation were studied in terms of morphological changes (light and electron microscopy) and also release of constituents (DNA and calcium ions) from the core of the spore. Spores which are highly resistant to conventional heating such as autoclaving were fragmented by microwaves, albeit only at a greater intensity than was required for spores of mesophilic species. Spores of B. sphaericus NCTC 9602 and of a mutant, which contains 30% of the dipicolinic acid (DPA) of the parent, showed identical profiles of disruption with respect to time and temperature. It is unlikely therefore that DPA plays any role in the thermal excitation of the core. The DNA liberated by microwaving spores was amplifiable by polymerase chain reaction; the rapid identification of spores in the food and pharmaceutical industries is thus possible using this approach.