Phage-displayed peptide libraries were used to map immunologically relevant epitopes on the surface (S) glycoprotein of a neurotropic murine coronavirus (MHV-A59). Three in vitro virus-neutralizing and in vivo protective mAbs against either continuous or discontinuous epitopes on the S glycoprotein were used to screen 12 different peptide libraries expressed on the pVIII major coat protein of the fd filamentous bacteriophage. Consensus sequences that matched short sequences within the S glycoprotein were identified. The sequence of a tight-binding, mAb-selected peptide suggested the location of a discontinuous epitope within the N-terminal S1 subunit. Several tightly binding phage were amplified and used directly as immunogens in BALB/c and C57BL/6 mice. Partial protection of C57BL/6 mice against a lethal acute virus infection was achieved with a phage preparation that displayed a linear epitope. Protection correlated with the presence of sufficient levels of specific antiviral antibodies recognizing the same immunodominant domain and 13-mer peptide, located within the C-terminal S2 subunit, as the selecting mAb. Thus, the direct use of phage-displayed peptides to evaluate protective antiviral immune responses complements their use to characterize antibody-binding epitopes. This is the first evaluation of protective immunization induced by mAb-selected phage-displayed peptides.