In the present state of knowledge of epidemic hepatitis, this disease can be defined only in descriptive terms, since the infectious agent has not yet been isolated and identified. The disease is transmissible to human beings by oral or parenteral inoculation with a filter-passing agent, presumably a virus,1 but in contrast to spirochetal jaundice and yellow fever experimental infection of animals has never been accomplished. It is characterized clinically by evidence of hepatic dysfunction and pathologically by inflammatory and degenerative changes in the hepatic parenchyma. It ordinarily runs a benign, self-limited course of two to three weeks' duration, but symptoms may persist for months, with or without acute recrudescences. Although the mortality is low, death may occur at any stage. On clinical and pathologic grounds it is indistinguishable from the endemic, sporadic disease known for many years as catarrhal jaundice, from homologous serum jaundice and from at least certain