Mice injected with drug or vehicle were administered a 13 mA shock via corneal electrodes. The number of mice in which the shock produced a tonic seizure was recorded. The dose that blocked seizures in 50% of mice (ED50) was determined for each drug. The drugs evaluated consisted of 15 hypnotics, two antidepressants and two antihistamines. All hypnotics and antidepressants, and one antihistamine, caused a dose-dependent suppression of seizures. The ED50's were highly correlated with hypnotic potency in man. The advantages of this procedure, as compared to others currently used for the evaluation of hypnotic potential of novel compounds, are discussed.