The immunological effector mechanism responsible for the elimination of virus in murine acute non-fatal extracranial lymphocytic choriomeningitis virus infection was studied. In this infection virus clearance is generally regarded as the result of a direct action of virus-specific cytotoxic T cells (Tc cells) on virus-producing target cells in the infected mouse. However, by manipulating the antiviral immune response by pretreatment with various doses of cyclophosphamide, we found lack of correlation between Tc-cell activity and the clearance of virus. In contrast, we observed a conspicuous correlation between the host's ability to mount a virus-specific delayed-type hypersensitivity (DTH) response and its capacity to combat virus. Moreover, pretreatment with silica and carrageenan prolonged viraemia without impairment of the peak Tc-cell response. These findings indicate that Tc cells have little or no capacity to eliminate virus, at least in the absence of an inflammatory response, and our findings suggest that virus clearance reflects a DTH-like process.