The effects of misonidazole (MISO) on brain stem evoked potentials (BAEPs) and cortical evoked potentials (CEPs) were evaluated in 16 Sprague-Dawley rats !reated with the agent. As found in previous studies, serial BAEPvalues were diagnostic of the onset of MISO toxicity before clinical signs and symptoms appeared. However, MISO had no effects on CEPs, which remained essentially unchanged through the course of the experiment. At histologic examination, significant changes were found in the area of the brain stem, but there was no histologic evidence of damage to cortical or subcortical structures caused by MISO administration. The results of this study suggest that the neurotoxic effects of MISO are species-specific, and that while the rat model may be useful for comparison of the relative toxic effects of nitroimidazole radiosensitizers, it is not a model suited for measurement of neurotoxicity caused by MISO in humans and nonhuman primates.A ddressfor reprints: Dr Edwards, c/o the Editorial Office,