Pre-clinical HIV-1 vaccine protocols, using multiple vaccine modalities and a potent adjuvant were assessed for vaccine efficacy in an experimental HIV-1 challenge model. C57Bl/6 mice were immunized with DNA plasmids encoding HIV-1 gp140, Gag and Tat alone or in combination with the corresponding recombinant proteins formulated in the adjuvant MF59. HIV-1 DNA alone or a DNA prime protein boost schedule resulted in complete protection against challenge with HIV-1/MuLV-infected murine cells. Although HIV-1 protein immunization in combination with MF59 resulted in partial protection, the DNA priming seemed to be crucial for obtaining full protection against the challenge. It is likely that the partial protection seen after immunization with protein alone is, to a certain extent, due to effects of the adjuvant since some animals that received the adjuvant MF59 alone were protected from the challenge. For the most part, antigen-specific cell-mediated immune responses as detected in the spleen (in contrast to responses detected in peripheral blood) of immunized animals appeared to be associated with protection in this study.