Prophylactic treatment with barbituric acid has been made for preventing severe hyperbilirubinemia in G-6-PD deficient newborn infants. In 17 out of 46 untreated and in 7 out of 171 treated cases exchange transfusions were needed since the biliriibin serum level exceeded 18 mg/100 ml. These data show that this prevention can be useful in areas, such as Sardinia, where the incidence of G-6-PD deficiency is very high. It has been further demonstrated that this particular form of neonatal hyperbilirubinemia is not due to increased red cell destruction.