AIM: To clarify the pathogenesis of ductular proliferation and its possible association with oval cell activation and hepatocyte regeneration.METHODS: Immunohistochemical staining and image analysis of the ductular structures in the liver tissues from 11 patients with severe chronic hepatitis B and 2healthy individuals were performed. The liver specimens were sectioned serially, and then cytokeratin 8 (CK8),CK19, OV6, proliferating cell nuclear antigens (PCNA),glutathione-S-transferase (GST), o-fetal protein (AFP)and albumin were stained immunohistochemically.RESULTS: Typical and atypical types of ductular proliferation were observed in the portal tracts of the liver tissues in all 11 patients. The proliferating ductular cells were positive for CK8, CK19, OV6 and PCNA staining.Some atypical ductular cells displayed the morphological and immunohistochemical characteristics of hepatic oval cells. Some small hepatocyte-like cells were between hepatic oval cells and mature hepatocytes morphometrically and immunohistochemically.CONCLUSION: The proliferating ductules in the liver of patients with severe chronic liver disease may have different origins. Some atypical ductular cells are actually activated hepatic oval cells. Atypical ductular proliferation is related to hepatocyte regeneration and small hepatocyte-like cells may be intermediate transient cells between hepatic oval cells and mature hepatocytes.