Progress in understanding myocarditis is being made on several fronts. Evaluation of the workability and significance of the Dallas criteria for the pathologic diagnosis of myocarditis will soon be available, and the sensitivity of the endomyocardial biopsy as a diagnostic tool in myocarditis is better understood. The viral hypothesis for human myocarditis has been revived. Further characterization of the cellular and humoral immunologic features of the human and murine diseases and the immunogenetic determinants of susceptibility has been carried out, and attempts to resolve uncertainties regarding therapy continue. Additional gains are being made in unraveling the murine enteroviral model. The fundamental histopathology of evolving lesions, the distribution of virus during the acute phase of the disease, the possibility of persistence, the diversity of host and virus genetics and their impact on the nature and severity of disease, the development of secondary (repeated) infection protocols that have led to further insights into pathogenesis, the study of mice with severe combined immune deficiency, and in vitro observations on the interaction of virus and host cells have provided new information.