The definition of non-A, non-B hepatitis (NANB) is improved by further characterization of what it is not (like the delta agent or non-A epidemic hepatitis) rather than by providing convincing evidence of isolation of the agent responsible for blood transfusion- or blood product-related NANB or specific markers thereof. Yet, NANB research is in disquieting movement. Modern biotechnology yielded its blessings to the field. However, monoclonal antibodies and molecular probes will have to be evaluated with the same scrutiny that unmasked so many test systems and viral agents thus far. Recent victims appear to be published reports on NANB being identified as a retroviral agent and NANB virus being propagated in primary cultures of chimpanzee hepatocytes. Yet the application of these powerful new tools, together with the availability of cultured human and chimpanzee hepatocytes for propagation of the agent may improve the chances for substantial progress. Our finding of involvement of lymphocytes in transmission of the disease may add another approach to reach the ultimate goal of characterization of the causative agent and development of diagnostic methods to detect it in patients and biological materials derived from carriers of the disease.