We evaluated EP HIV-1090 vaccine, a DNA plasmid encoding 21 cytotoxic T-lymphocyte (CTL) epitopes of human immunodeficiency virus type 1 (HIV-1) and the pan-DR helper T-lymphocyte epitope (PADRE), in a dose escalation, randomized, double-blinded, placebo-controlled Phase 1 trial. Vaccine, at 0.5, 2.0, or 4.0mg doses, or placebo was injected four times over 6 months. Forty-two healthy, HIV-1-uninfected adults were enrolled. Using an interferon-gamma ELISPOT assay, a response to PADRE was detected in one vaccine recipient. Three vaccine recipients raised anti-HIV-1 CD8+ CTL measured by chromium-release assay. The vaccine was safe and well-tolerated, but only weakly immunogenic.