Liver biopsies from 86 patients with serologically established acute hepatitis A were evaluated for quantitative and qualitative light microscopic features together with biopsies from 78 patients with acute hepatitis type B and 76 patients with acute hepatitis type non-A, non-B. Hepatitis A was characterised by more pronounced portal inflammation than hepatitis non-A, non-B (p less than 0.01) but less conspicuous parenchymal changes (focal necrosis, Kupffer cell proliferation, acidophil bodies, ballooning) than found in hepatitis type B (p less than 0.01). Steatosis occurred in 10% of the hepatitis A biopsies compared with 26% (p less 0.01) and 6% (not significant) in the hepatitis non-A, non-B and B groups, respectively. A comparison between the histological findings in women and men revealed that iron deposits occurred in more than half of the men compared to less than 20% of the women (p less than 0.01) irrespective of hepatitis type. Histological and biochemical follow-up was available in 36 patients with hepatitis A. For the majority of these patients the bilirubin concentration reached normal values within one month of the initial biopsy. The activity of serum transaminases showed good correlation with the degree of histological resolution. Non-specific reactive hepatitis with slightly raised serum transaminases were often seen during recovery from hepatitis A. These patients may be misinterpreted as cases of acute non-A, non-B hepatitis.