In an effort to lower the incidence and severity of neconatal jaundice, 96 mothers were each given 20 mg of phenobarbital each night, beginning at the thirty-second week of gestation. Previous reports have suggested that such treatment stimulates the glucuronyl transferase system in the fetal liver and lowers the incidence of hyperbilirubinemia in the newborn. Serum bilirubin levels during the first four days of life were compared with those of 114 control mothers and infants. Treatment lowered the mean neonatal bilirubin at 72 hours after birth from 8.5 to 6.4 mg%. While 24.6% of control infants had serum bilirubin levels greater than 10 mg % at 96 hours, only 7.3% of the treated infants had levels greater than 10 mg % at this time. This study concludes that treating mothers with phenobarbital is an effective adjunct in lowering the incidence of neonatal jaundice.