The work of Julian Herman Lewis helps to expose the underlying racial organization of laboratory normality in early twentieth-century medicine. In the 1920s and 1930s, Lewis launched a critique of prevailing racial theory, as he established an academic career in pathology at the University of Chicago. As one of the small number of black research physicians at the time, Lewis met barriers to his work that eventually derailed his career. Although his research fell short of its goals, his work continues (...) to provide a key insight into medical laboratory standards as they became institutionalized in Lewis’s field of clinical pathology. By avoiding attributions of race and following prevailing practices of racial exclusion, medical laboratories quietly reasserted social norms in the formation of laboratory normality. An examination of Lewis’s critiques and his research sharpens questions about the development of the concept of “normal” in the human sciences and a related tendency in twentieth-century medicine to conflate difference with pathology. (shrink)