AbstractReplication of duck hepatitis B virus in extrahepatic tissue such as pancreas, kidney and spleen has been well documented. To assess whether there is more widespread extraheptic virus replication, we assayed brain, heart, lung, thymus, pancreas, kidney, spleen and intestine of 1‐ to‐wk‐old ducklings for the presence of duck hepatitis B virus DNA and mRNA by blotting inin situmethods. Replicative intermediates and single‐stranded duck hepatitis B virus DNA and RNA transcripts were detected in the brain, lung, heart, intestine, kidney, pancreas and spleen. In situ hybridization showed evidence of viral replication in the lung epithelium, germinal center of spleen, acinar cell of pancreas and tubular epithelium of kidney.These data suggest that extrahepatic duck hepatitis B virus replication is more widespread than previously thought. It is yet to be determined whether widespread extrahepatic replication is unique to duck hepatitis B virus infection or is a common feature of other mammalian hepatitis B‐like viruses. (HEPATOLOGY 1990; 1