Seizures and status epilepticus, which may contribute to brain injury, are common consequences of exposure to organophosphorus (OP) cholinesterase inhibitors. Effective management of these seizures is critical. To investigate the efficacy of nasal midazolam as an anticonvulsive treatment for OP exposure, as compared to intramuscular midazolam, guinea pigs were connected to a recording swivel for electrocorticograph (ECoG) monitoring and clinical observation. The experimental paradigm consisted of pyridostigmine pretreatment (0.1 mg/kg i.m.) 20 min prior to sarin exposure (1.2x LD50, 56 μg/kg i.m.). One minute postexposure, atropine (3 mg/kg i.m.) and TMB-4 (1 mg/kg i.m.) were administered. Within 3-8 min after sarin exposure all animals developed electrographic seizure activity (EGSA), with convulsive behavior. Treatment with midazolam (1 mg/kg i.m.) 10 min after the onset of EGSA abolished EGSA within 389 ± 181 s. The same dose was not effective, in most cases, when given 30 min after onset. However, a higher dose (2 mg/kg) was found efficacious after 30 min (949 ± 466 s). In contrast, nasal application of midazolam (1 mg/kg) was found most effective, with significant advantages, in amelioration of EGSA and convulsive behavior, when given 10 min (216 ± 185 s) or 30 min (308 ± 122 s) following the onset of EGSA (P < 0.001). Thus, nasal midazolam could be used as a novel, rapid and convenient route of application against seizure activity induced by nerve agent poisoning.