Formalin fixed liver, spleen, kidney, heart, lung, duodenum and appendix tissues from nine rabbits, experimentally infected with rabbit haemorrhagic disease virus (RHDV), were investigated for evidence of RHDV antigen by the direct avidin-biotin peroxidase complex immunohistochemical method. In all the rabbits examined, RHDV antigen was detected in degenerative and necrotic hepatocytes of the liver tissues. The area involved coincided with histopathological lesions on serial liver sections. The RHDV antigen was expressed in the cytoplasm of the hepatocytes, suggesting that RHDV replicated in these cells. RHDV antigen was also detected in the spleen. The results of immunohistochemistry were supported by the demonstration of RHDV protein by Western blot analysis and of RHDV particles by protein A-gold immunoelectron microscopy in the liver homogenate from all the rabbits that were examined.