Studies of the controls over the expression of the latent C type viruses found in all chickens will be carried out. Similar viruses are ubiquitous in nature, are found in all animal species studied in depth and very likely occur in man as well. Their role as host genetic elements and in spontaneous tumor formation must be elucidated. Other research with avian tumor viruses has included investigation of virus structure and replication and study of the properties of virus transformed cells, and these studies will continue. Human hepatitis B has also been investigated and a virus-like particle with hepatitis B antigen on its surface has been identified which contains a small circular double stranded DNA and DNA polymerase. Studies to show that this particle is the infectious virus of hepatitis B will include tissue culture and animal inoculation. Eventually the role of this virus in chronic diseases associated with hepatitis B antigen such as chronic active hepatitis and hepatoma will be investigated.