A histochemical-morphometric method was used to measure potassium (K+) levels in gray and white matter of rats following sublethal intoxication with 11 different neurotoxic compounds of high forensic significance. Six rats were each given a single substance applied intraperitoneally, the same dosage being given to two animals each. The animals were subsequently killed, the brains immediately frozen, and cryosections cut. K+ levels were evaluated morphometrically. A drop in K+ levels was used as the criterion for cytotoxic edema. Application of ethanol, atropine, carbromal, carbon monoxide, morphine or triethyltin led to a rise in K+ levels in the gray matter and a simultaneous decline in the white matter. By contrast, administration of amitriptyline, glycerin, potassium cyanide, parathion or phenobarbital initiated an increase in K+ levels in both gray and white matter. A cytotoxic edema could thus be reliably excluded in these intoxications. Although the study design allows no statistical analysis, these conclusions are supported by the marked differences in K+ levels in gray and white matter induced by the different toxicants.