Attempts to identify non-A, non-B hepatitis agents by serologic means have been uniformly unsuccessful throughout the world. We have sought to apply recent advances in nucleic acid chemistry to a search for the genome of the non-A, non-B agent. Sensitive radiolabeling procedures have been modified to permit labeling of minute quantities of nucleic acid. Identification of the genome of the non-A, non-B agent would permit its characterization and cloning.