INTRODUCTION 1-Epidemic hepatitis has attained pandemic proportions during this war. Large outbreaks have occurred in many parts of the world and in the armies of a number of nations.'23 The pathology of this disease as observed in the Army of the United States during the epidemic of 1942 has been dealt with in previous papers. 24'25 More recently, an acute form of epidemic hepatitis of intense severity terminating fatally in less than io days has. become prevalent; this we have termed the fulminant form. In a new series of i96 fatal cases occurring between August, I943, and April, I945, which we have studied at the Army In-stitute of Pathology, over half fall into this category. By contrast, in the previous series not a single equally fulminant case was encountered, and only one was reported in the great Swedish epidemic of I927; 26 the usual duration of the fatal disease was then from 4 to 6 weeks; in other words, the course of fatal hepatitis was predominantly subacute. These divergences in duration reflect striking differences in the perti-nent pathologic changes. Thus, in the more fulminant form, the par-enchyma of the liver is destroyed completely and uniformly, and this destructive process is accompanied by an intense inflammatory reac-tion. In the more subacute form seen in I942 and also in approximately one-fourth of the I943-I945 series, destruction of" the liver is incom-plete, the involvement characteristically not uniform, regenerative hyperplasia of surviving parenchyma leads to the production of much new tissue, and inflammation is less pronounced. Another significant difference is in the epidemiology. In 1942, hepatitis in many instances followed administration of yellow fever vaccine containing human serum. In the new series, such vaccine had not been used; but nearly one-half of the patients had sustained combat trauma. Since seriously wounded patients customarily received transfusion of whole blood, serum, or plasma, it may be assumed that a high proportion of the wounded in this series were thus treated. But it isnot known in how many the causal agent of hepatitis was introduced by therapeutic procedures, especially as in several theaters of war large epidemics of hepatitis were prevalent. It is, therefore, an assumption to regard all the wounded cases as examples of" homologous serum hepatitis." This assumption is justified largely by the rela-tively long interval between date of wound (and presumably of first. transfusion) and the clinical manifestation of the disease. The non-wounded cases, comprising approximately one-half of the series, repre-sent both the epidemic and the endemic variants of" naturally" occur-ring hepatitis.