The macroscopic, light microscopic and electron microscopic features and biological properties of MC-29 virus-induced hepatocellular carcinomas in chickens are described. The tumors developed in noncirrhotic livers within a very short time and formed metastases. Virus production was also evidenced in the tumors. There were also indications of virus production in the transplantable tumors. The tumors grew equally well after sc, ip, or im inoculation. In about 25% of the tumor-bearing animals, tumorous nodules developed in the liver. It could not be established whether they were metastases or primary liver cancers induced by viruses released from the transplantable tumors.