T-cell epitopes of porcine reproductive and respiratory syndrome virus (PRRSV) glycoproteins 4 (GP4), 5 (GP5) and nucleocapsid (N) were predicted using bioinformatics and later tested by IFN-γ ELISPOT in pigs immunized with either a modified live vaccine (MLV) or DNA (open reading frames 4, 5 or 7). For MLV-vaccinated pigs, immunodominant epitopes were found in N but T-epitopes were also found in GP4 and GP5. For DNA-immunized pigs, some peptides were differently recognized. Using a large set of PRRSV sequences it was shown that N contains a conserved epitope and that for GP5, the genotype-I counterparts of previously reported epitopes of genotype-II strains were also immunogenic.