The D variant of encephalomyocarditis virus (EMCV-D) induces a diabetes mellitus-like disease in male SJL/J mice. Other inbred strains, while resistant to the diabetogenic effect, exhibit strikingly different responses to this virus. In these studies, infection of diabetes resistant C3H mice with the D variant produces massive acute pancreatitis with little apparent direct islet cell involvement. This exocrine tropism is not altered when C3H mice with an inherent macrophage defect are infected, and appears to be a gender-specific phenomenon, with female C3H mice resistant to this exocrine involvement. Long-term infection of both male and female C3H mice does not change their response to the virus. Castration of male C3H mice, using a protocol that has been reported to block the diabetogenic effect of this virus, does not alter the development of this acinar lesion. The B variant of EMCV does not induce acinar destruction, nor is it diabetogenic. However, preinfection with the B variant 3 days prior to infection with the D variant does protect against the development of the exocrine lesion. Coinfection with equal doses of the two variants also protects against this lesion, as does coinfection with a lower dose of B variant. Therefore, the host response that is generated against the B variant appears to be responsible for this protection from D variant exocrine destruction. Due to the short time frame, it is unlikely that this protection is the result of an antibody response. Rather, this data is more consistent with an interferon response generated against the B variant that would inhibit replication of the D variant.