We studied 14 newborn infants with seizures after birth asphyxia or other causes. Paraldehyde was given as a 200 mg/kg IV bolus followed by an infusion of 16 mg/kg/h (10 cases), or as a 400 mg/kg bolus (4 cases). Serum concentrations of paraldehyde were higher in periods of adequate seizure control than in periods of little or no response. Paraldehyde serum concentrations above 10 mg/dl were associated with anticonvulsant effects and were achieved in most neonates with a 2-hour infusion of 200 mg/kg/h. If there is no effect, serum concentrations are probably below 10 mg/dl and an additional 200 mg/kg can be given safely over 1 hour.