The classification of chronic hepatitis introduced in 1968 is still current, but has been modified. The concept of bridging hepatic necrosis has been incorporated, and is recognised as an important feature of both acute and chronic aggressive (active) hepatitis (CAH). In the pathogenesis of the latter, piecemeal necrosis is, however, thought to be the more important factor. The histological picture of CAH varies widely. Several causes of CAH have been identified, including hepatitis B virus. Recognition of surface and core components of the virus in tissue sections has facilitated study of the relationship between host response and pathological lesion in chronic hepatitis. CAH and primary biliary cirrhosis share histological features, and a mixed form has been postulated. Staining for copper sometimes helps to distinguish the two lesions. A third histological category, chronic lobular hepatitis, comprises patients with histological lesions like those of acute hepatitis, but with a chronic or recurrent course.