The incidence of haematological abnormalities has been evaluated in 1170 patients affected by acute viral hepatitis. Of these patients, 665 were HBsAg+, 427 HBsAg-, 31 with IgM anti-HAV, 26 non A and non B hepatitis. 21 patients were not classified due to lack of data relating to markers for HAV or HBV. Anemia, leucopenia, thrombocytopenia and pancytopenia were found with some frequency at the haemochromocytometric examination. It is emphasized that these haematological abnormalities are often of minor relevance whereas the rarer and more serious complications such as persistent bone marrow hypoplasia or pure aplastic anemia can present difficult clinical problems regarding prognosis and therapy: in 4 cases of bone marrow hypoplasia a recovery was obtained in 1 case only, whereas the remaining cases had a fatal outcome after a period varying from 20 days to 15 months from the appearance of pancytopenia. We suggest the advisability of a closer study of the haematological and immunological aspects in patients with viral hepatitis in order to discover those elements which are useful towards a better understanding of the etiopathogenesis of the haematological abnormalities studied above. Such a detailed study would also enable further improvement in existing therapeutic measures.