The effect of pentobarbital, given to the mother, on maternal and fetal blood gas tensions was examined. Pentobarbital anesthesia reduced the rate of acid accumulation during asphyxia in fetal monkeys, increased the duration of primary apnea and of gasping, accelerated the establishment of rhythmic breathing on resuscitation, and reduced the incidence and severity of permanent brain damage assessed by histologic examination. © 1969 The C. V. Mosby Company.