Relapsing-remitting experimental allergic encephalomyelitis (R-EAE) is an animal model for multiple sclerosis (MS). Many potential immunomodulatory strategies for MS have been used first in EAE to assess their effectiveness. Recently, the injection of plasmid DNA has been shown to induce potent humoral and cellular immune responses. The primary aim of our experiments reported here was to determine if vaccination with cDNAs encoding myelin proteolipid protein (PLP) could prime for a PLP-specific immune response and affect subsequent R-EAE. We constructed cDNAs encoding whole PLP (pPLP(all)) or encephalitogenic epitopes PLP(139-151) (pPLP(139-151)) and PLP(178-191) (pPLP(178-191)). Following DNA injection, we induced R-EAE in SJL/J mice using PLP(139-151) or PLP(178-191) peptides in adjuvant. All 3 plasmid constructs enhanced R-EAE induced with PLP(139-151), and injection of mice with pPLP(all) increased R-EAE induced with PLP(178-191). DNA immunization induced higher PLP peptide-specific lymphoproliferative responses than did vector alone following R-EAE induction with IgG1 or IgG2b antibody responses. These data suggest that DNA immunization of PLP can modulate immune responses, leading to enhancement of R-EAE.