During the period comprised between March to May, 1981, 3 out of 435 inhabitants of the locality of Julio Zawady. Cienaga county, Magdalena Departament, Colombia, died after a short febrile, acute and severe disease leading to hepatic comma. Another patient survived after 8 days illness. The histopathological diagnosis on the liver of the only autopsied case was of Fulminant Hepatitis. Sierra Nevada de Santa Marta Type. p Hepatitis A and B antigenic markers were studied in 71 apparently healthy people related and unrelated to the cases of the above mentioned and two others neighboring localities, as follows: 1. Ninety nine per cent of the tested sera were positive for anti-HA-Ag. 2. Thirty nine per cent were positive for HBsAg and/or HBeAg; the group of 5 to 9 years of age was positive in 53%. 3. Only 14 sera were tested for anti-HBeAg of which 78% were positive. It is then possible to suggest that the etiologic agent of the disease was the Hepatitis B virus. On the other hand, no relevant observations were found concerning the natural history of the disease and its relation to the macro or micro-enviromment. Finally it reamains unknwown why this virus behaves so aggressively and yields a high mortality rate.