Recently we reported regional levels of norepinephrine and dopamine in rat brain following microwave irradiation. In our report, we also compared these levels with those of norepinephrine and dopamine following decapitation. Catecholamine levels following exposure to microwave irradiation significantly increased in several areas. However, whether these increases resulted from compound transfer associated with tissue disruption due to high intensity microwave irradiation was not determined. Sections of corpus striatum and locus coeruleus were examined with a light microscope and the interface of the striatum and the cortex showed no trace of tissue breakdown. Transformed cells, vacuolation, and indications of pyknotic degeneration in the nucleus were found in locus coeruleus after irradiation, but the shapes of these cells were well-defined. Electron microscopic photographs of synapses in the same area showed membrane damage after exposure for 5 s at 1.3 kW, but synaptic vesicles were clearly defined. It was concluded that the increased catecholamine levels were not the result of tissue disruption following rapid heating of the brain by irradiation.