Mouse hepatitis virus, strain JHM, is a coronavirus capable of inducing both acute and chronic central nervous system disease. To characterize the cell-mediated immune response directed toward JHMV antigens, we have generated and analyzed the properties of four T cell clones reactive to JHMV antigens. All four clones are of the Ly-1+2- phenotype and show an antigen-specific, I-Ab-restricted proliferative response that is dependent on antigen-presenting cells (APC). The fine specificity of I-A restriction was revealed by their differential recognition of JHMV antigen in the context of mutant I-A molecules present on B6.C-H-2bm12 APC. Two clones were unable to recognize JHMV antigen presented on bm12 APC, whereas a third clone showed an equivalent response with both bm12 and wild type B6 APC. In the analysis of the viral specificity, three of the clones showed distinct cross-reactions with MHV-2 and very little if any cross-reaction with MHV-A59. In addition, three of three clones tested responded well to sucrose gradient-purified, UV-inactivated JHMV, indicating that their specificity is directed toward virus structural rather than nonstructural proteins. Finally, two of the clones were analyzed for their ability to induce a DTH reaction when injected together with antigen into the footpads of various mouse strains. Consistent with the in vitro data, both clones produced a marked DTH response only in those strains carrying the I-Ab genotype. These data demonstrate, both in vivo and in vitro, that at least one component of the cell-mediated immune response to JHMV is characterized by an Ly-1+2-, I-A-restricted T cell specific for JHMV structural proteins.