The authors call attention to the epidemic-endemical character of Leptospirosis occurring in the city-state of Guanabara (Rio de Janeiro - Brasil) and its surroundings. They lay down data concerning both the severity of the infection and the poor knowledge of the anicteric form of the disease. They further emphasize the digestive manifestations of Leptospirosis as well as the importance of inserting this condition ín the differential diagnosis of the "surgical-abdomen", chiefly when jaundice is also present. They regard such findings as anuric acute renal failure, digestive tract hemorrhages, convulsions and/or shock as valuable indications of a very poor prognosis. Among the digestive manifestations of the disease, the authors have specially stressed hepatic involvement and of course, jaundice. The presenting material is made up of 42 cases of Leptospirosis, which have been thouah"ouly studied both from a functional and a histopatholoçical standpoint. The material was obtained through biopsy-puncture except for 3 cases, which were cutopsied. The deepest jaundice was found about the 2nd and 3rd weeks in the course of the disease and the preválente fraction of the hyperbilirubinemia was the "direct one". Fairly high serum allcaline phosphatase and chólesterol, side by side with severe hyperbilirubinemia, occurring at the 2nd and 3rd weeks in the course of the disease gave clue to the presence of an important obstruetive component, which proved to be the fact through the histopathologioal findings. In no instance have the transaminase levels exceeded 250 Karmen units. No important hepatic necrosis toas found in any of the histopathological specimens examined. Prothrombinic activity less than 60% was found in 22 patients and those who were given vit. Kl showed no response whatsoever. The chief protein electrophoretic changes found in 26 patients were as follows: hypoalbuminemia and high alpha-2 fraction in all of them; beta-fraction over 0.90 g% in 14 patients; gamafraction over 1.4 g% in 15 patients. Both the flocculation and turbidity tests showed fairly significant changes in 14 patients. The chief pathological changes found were: predominance of centro-lobular lesions, trabecullar derangement, cholestasis, degenerative as well as regenerative changes of the main liver cells, and, hyperplasia of Kupffer cells. Such findings can be obtained in patients after a period of 30 days from the initial symptoms. Finally, the authors analyse the pathogenical features of the disease as well as the physiopathology of hepatic lesions in the course of Leptospirosis.