The hepatic abnormalities that developed after the splenectomy in 10 subjects with idiopathic myelofibrosis were analyzed. In all patients in whom a liver biopsy was performed during the splenectomy, extramedullary hematopoiesis was demonstrated, consisting of dysmorphic megakaryocytes primarily localized in the sinusoids, often accompanied by erythroid precursors. Following splenectomy, a significant increase in both the liver size and serum levels of alkaline phosphatase, bilirubin or gamma-glutamyl transpeptidase was found within 6 months, whereas no such increase was observed in the serum aspartate transaminase and alanine transaminase concentrations. In addition, 2 patients developed acute liver failure leading to death at 3 and 4 weeks from splenectomy, respectively. In contrast with these findings, no hepatic alterations were observed in 10 chronic myeloid leukemia patients who were also submitted to splenectomy.