Recent reports from Sardinia, Greece and Malaya indicate that glucose-6phosphate dehydrogenase (G-6PD) deficiency may constitute an important aetiological factor in the causation of severe neonatal jaundice and kernikterus (Panizon, 1960a, b; Doxiadis, Fessas and Valaes, 1961; Smith and Vella, 1960; Weatherall, 1960). Since this enzyme deficiency is very frequent in certain oriental Jewish communities in Israel (Szeinberg, Sheba and Adam, 1958; Sheba, Szeinberg, Ramot, Adam and Ashkenazi, 1962), a high incidence of severe jaundice of newborn not due to iso-immunization could be expected to occur in this country. If this were the case, a considerable disadvantage to carriers of this trait, even under natural conditions (without intake of drugs), would have to be assumed. From the practical point of view such a finding would necessitate the establishment of large-scale facilities for exchange transfusion in the areas inhabited by population groups with a high frequency of G-6PD deficiency. A preliminary inquiry among paediatricians in several hospitals did not reveal any awareness of a difference in frequency of severe jaundice and transfusions between Oriental and European (Ashkenazi) Jewish communities. However, in view of the findings in other countries listed above, we decided to investigate this problem more closely.t