Non-viral in vivo administration of plasmid DNA for vaccines and immunotherapeutics has been hampered by inefficient delivery. Methods to enhance delivery such as in vivo electroporation (EP) have demonstrated effectiveness in circumventing this difficulty. However, the contact-dependent nature of EP has resulting side effects in animals and humans. Noncontact delivery methods should, in principle, overcome some of these obstacles. This report describes a helium plasma-based delivery system that enhanced humoral and cellular antigen-specific immune responses in mice against an intradermally administered HIV gp120-expressing plasmid vaccine (pJRFLgp120). The most efficient plasma delivery parameters investigated resulted in the generation of geometric mean antibody-binding titers that were 19-fold higher than plasmid delivery alone. Plasma mediated delivery of pJRFLgp120 also resulted in a 17-fold increase in the number of interferon-gamma spot-forming cells, a measure of CD8+ cytotoxic T cells, compared with non-facilitated plasmid delivery. This is the first report demonstrating the ability of this contact-independent delivery method to enhance antigen-specific immune responses against a protein generated by a DNA vaccine.