Heterologous immunity associated with cross-reactive T-cell responses is proposed to contribute to variations among individuals in the pathogenesis of human viral infections. In genetically identical mice with similar infection histories, marked variations in the magnitude and specificities of T-cell responses under conditions of heterologous immunity occur and have been linked to the private specificity of T-cell repertoires in individual immune mice. Variations in immunopathology in the form of panniculitis are observed in lymphocytic choriomeningitis virus-immune mice after vaccinia virus infection. By adoptively transferring splenocytes from individual lymphocytic choriomeningitis virus-immune donors into paired recipients, we show here that, on vaccinia virus infection, similar levels of panniculitis were generated in recipients from a single donor, but the severity of panniculitis varied among recipients receiving cells from different donors. This indicates that virus-induced immunopathology under conditions of heterologous immunity is a function of the private specificity of the immune repertoire.