Diazepam (Valium) proved to be effective in preventing local anesthetic-induced convulsions. In cats with recording electrodes permanently implanted in the brain, the median intravenous convulsant dose of lidocaine (CD50) was 8.4 mg/kg. One hour after pretreatment with 0.25 mg/kg of intramuscular diazepam, the lidocaine CD50doubled to 16.8 mg/kg. This dose of diazepam had no discernible effect on behavior or EEG. However, larger doses of diazepam (0.33 and 0.5 mg/kg) caused ataxia and shifted the EEG to slow high-voltage patterns—without appreciably improving protection against seizures.