The features of seizure-related brain injuries in rats poisoned i.p. with diisopropylfiuorophosphate were investigated. Pyridostigmine bromide (0.1 mg/kg) and atropine methylnitrate (20 mg/kg), which are centrally inactive, were pretreated i.m. 30 min and 10 min, respectively. before diisopropylfluorophosphate (10 mg /kg, $2LD_50$) poisoning to reduce the mortality and eliminate peripheral signs. Diisopropylfluorophosphate induced severe limbic seizures, and early necrotic and delayed apoptotic brain injuries. The necrotic brain injury, which was closely related to seizure intensity, was exerted as early as 1 hr predominently in hippocampus and piriform cortex. showing spongiform change (malacia) of neurophils in severe cases, in contrast to a typical apoptotic (TUNEL-positive)pattern after 12 hr in thalamus, and a mixed type in amygdala. Nitric oxide content in cerebrospinal fiuid significantly increased after 2 hr, reaching a maximal level at 6 hr. Pretreatment with $_L-N^G$-nitroarginine, an inhibitor of nitric oxide synthase, reduced nitric oxide content and attenuated only apoptotic brain injury in all four brain regions examined without affecting seizure intensity and necrotic injury. Taken together, early necrotic and delayed apoptotic brain injuries induced by diisopropylfiuorophosphate poisoning in rats may be related to seizure intensity and nitric oxide production, respectively.