A requisite for vaccines to confer protection against intracellular infections such as Human Immunadeficiency Virus or Mycobacterium tuberculosis is their capacity to induce Th1 immune responses. However, they may fail to do so in Africa and South East Asia, where most individuals have a dominant preexistent Th2 immune profile, due to persistent helminthic parasitic infections, which may undermine any Th1 response. It is well established that DNA vaccines induce strong Th1 biased immune responses against an encoded antigen, depending on the route and mode of immunization. Here, we demonstrate that intradermal immunization with plasmid DNA encoding p-gal (pCMV-LacZ) of Schistosoma-infected mice, with preexistent dominant Th2 immune background, induce a strong Th1 anti-beta -gal response, as opposed to immunized with beta -gal only. Importantly, the established protective Th2 immune response to schistosomes was not disrupted. These findings strongly support the possibility of using plasmid DNA as a Th1 inducing adjuvant when immunizing populations with a strong preexistent Th2 immune profile.