Coxsackie B viruses are a common cause of viral myocarditis in humans. A murine model of the human disease has been developed using Coxsackievirus group B, type 3 and inbred Balb/c mice. Infection of T lymphocyte deficient mice does not result in significant myocarditis indicating the importance of T cells in this disease. The virus can be isolated from the hearts of T cell deficient and normal mice in equal concentrations. Virus elimination presumably is mediated by virus specific neutralizing antibody induced in both groups. T lymphocytes, natural killer cells and macrophage obtained from normal virus infected mice are all capable of lysing myofibers in vitro. Maximum lysis is obtained with the cytolytic T cells. When these cell populations or Coxsackievirus immune antibody were adoptively transferred into T lymphocyte deficient animals infected with the virus, only animals given T cells developed significant myocarditis.