Two cases of familial nonhemolytic jaundice have been described. Both patients, though severely jaundiced for periods of 5 and 2 years, have grown and developed normally and show no evidence of damage of the nervous system. This is in contradistinction to the six other patients, presented in the original report of this disease, who died after developing kernicterus. No reasons can be suggested for the escape of these two patients from kernicterus. Some speculations concerning the nature of the genetically controlled aberration in this disease have been given. It is suggested as a plausible hypothesis that the lesion consists of deficiency of an enzyme which controls the chelation of indirect-reacting bilirubin so as to form direct-reacting bilirubin. The enzyme, though deficient, is capable of adequate function if a sufficient load of bilirubin is presented to the liver. Under such circumstances bilirubin is excreted in normal amount, but only in the presence of a large accumulation of the pigment in the blood.