Common usage prescribes a single normal range for serum bilirubin levels. However, we have not only confirmed that men have higher levels than women but have discovered significant racial differences as well. Among 1,538 healthy Americans, blacks had lower mean bilirubin levels than whites of European origin, Latin Americans, and Asians. These racial differences, which were more pronounced among women than men, were maintained in pernicious anemia. Even though bilirubin levels rose in our 174 patients with this disease, they continued to be lower among blacks than among whites and Latin Americans. Moreover, the actual bilirubin level changes caused by pernicious anemia were themselves smaller among blacks. The racial differences, thus, persisted in pernicious anemia despite similar degrees of anemia, whereas the sex differences disappeared. We suggest that the lower serum bilirubin levels in blacks in health and disease do not stem primarily from lower bilirubin production than in whites.