This invention provides a DNA vaccine which comprises a naked DNA incorporating and expressing in vivo a nucleotide sequence encoding an antigenic polypeptide, preferably a gene of a pathogenic agent, and at least one adjuvant compound chosen from the polymers of acrylic or methacrylic acid and copolymers of maleic anhydride and alkenyl derivative. The adjuvant compound is preferably a carbomer or an EMA.RTM.. This invention also provides a method of enhancing a DNA vaccine and/or the immunogenicity of a DNA vaccine.