In less than ten years, two very serious viral hepatic diseases have spread through Leporidae populations (rabbits and hares) in numerous countries. In May 1989, the Office International des Epizooties designated this new disease of rabbits "viral haemorrhagic disease" and entered it as a List B disease in the International Animal Health Code. Clinically, the disease is very similar to the European brown hare syndrome. However, numerous uncertainties prevail today on the true nature of the viruses of the two species. Although they are related, the viruses appear to be different and cross infection between species has given contradictory results. Hepatitis of Leporidae have probably existed in Europe for several years, although their viral aetiology has been demonstrated only recently. The acute form has occurred in hares in Northern Europe since approximately 1980, while the inapparent (or ignored) form has been present in rabbits in Czechoslovakia since 1975. These diseases of Leporidae are true viral hepatitis which, in their fulminating forms, bear a remarkable resemblance to human viral hepatitis (B and non-A non-B) with regard to clinical symptoms, pathological lesions and mode of transmission. The dominant faecal-oral transmission observed for types A and E hepatitis would explain the particular susceptibility of family-kept rabbits, as they are fed potentially contaminated fodder. As the clinically similar fulminating hepatitis in human beings is caused by a diversity of viruses (both RNA and DNA), the disease in Leporidae might also be caused by different viruses.(ABSTRACT TRUNCATED AT 250 WORDS)