Unlike many other pathogens, there is limited knowledge of the specific PRRSV-derived peptides targeted by T-cells. In the current study, we report the identification of CTL epitopes from the PRRSV (Ch-1a strain) M protein in a mouse model. We screened peptides derived from the PRRSV M protein for their ability to induce interferon (IFN)-γ in splenocytes harvested from BALB/ c mice following DNA vaccination and a booster vaccination with recombinant vaccinia virus expressing M protein. The screen identified two peptides that elicited IFN-γ production in CD3 + CD8 + splenocytes of vaccinated mice. A multiple amino acid sequence alignment among different PRRSV M proteins indicates that these two peptides are strongly conserved across multiple PRRSV strains and therefore should be considered for further research.