Non-A non-B (NANB) hepatitis is a major cause of liver disease in both the developed and undeveloped countries of the world. While a large body of data strongly suggests an infectious agent, efforts to isolate such an agent have thus far not been rewarding. This proposal outlines steps which take advantage of the power of new techniques in molecular biology to clone DNA and/or RNA sequences from this infectious agent without the need for cell culture of what is apparently a very fastidious agent. Full-length cDNA clones will be isolated, placed in bacterial expression vectors, and used to generate peptides corresponding to their coding sequences. These peptides will be used as antigens both for generation of monoclonal antibodies and for direct use in diagnostic testing.