The incidence and distribution of necrotic and apoptotic neural cells, and activated astrocytes in the brain of rats intoxicated intra peritoneally with diisopropylfluorophosphate were investigated. Pyridostigmine bromide (0.1 mg/kg) and atropine methylnitrate (20 mg/kg) were pretreated intramuscularly 30 min and 10 min, respectively, prior to diisopropylfluorophosphate (4-10 mg/kg) administration. Diisopropylfluorophosphate induced severe limbic seizures, early necrotic and delayed apoptotic brain injuries, and rapid astrocytic responses. The necrosis, which was closely related to seizure intensity, was observed as early as 1 hr after intoxication predominently in hippocampal pyramidal cells, cerebellar Purkinje cells and neurons in pyriform/entorhinal cortices, showing malacia of neurophils. In contrast, apoptosis started to appear 12 hr after intoxication in neurons in thalamus, amygdala and neocortex, and ephendymal cells surrounding the 4th ventricle. Since marked apoptosis was induced in rats exhibiting relatively-low seizure intensity, the degree of necrosis and apoptosis was shifted to each type of injury according to the seizure intensity. Activated astrocytes, observed within 1 hr along the limbic system, were suggested to affect the neural injury patterns by producing high level of nitric oxide. However, the distribution of activated astrocytes was not in parallel with those of necrotic or apoptotic injuries, implying that the astrocytic responses resulted from seizure activity rather than neural injuries. Furthermore, astrocytes in malacic tissues disappeared during the severe limbic seizures. Therefore, it would be one of the cautionary notes on the expression of glial fibrillary acidic protein in astrocytes as a biochemical marker of brain injuries following acute exposure to organophosphates.