Objectives:To develop a peptide‐based model for a preventive vaccine for HIV‐1 infection.Design:Phase I trial in HIV‐1‐seronegative volunteers.Participants:Adult healthy subjects HIV‐1‐antibody‐seronegative in an enzymelinked immunosorbent assay, screened for tuberculin [purified protein derivative (PPD)] reactivity with 2 tuberculin units PPD‐administered intradermally.Interventions:Submicrogram doses of a PPD conjugate with a peptide of the primary neutralizing domain (PND) of HIV‐1MN(PPD‐MN‐PND) were administered intradermally to tuberculin skin‐test‐positive and ‐negative volunteers.Results:Antibodies to the MN‐PND were measured after two immunizations in 10 out of 11 PPD skin‐test‐positive volunteers. After the fourth immunization high‐affinity antibodies were detected, which persisted for over 1 year. High titers of MN‐PND‐specific immunoglobulin (Ig) G and IgA were detected in the serum and saliva of all volunteers tested. Serum antibodies were cross‐reactive with PND peptide from some other HIV‐1 strains but neutralized only the HIV‐1MNprototype. Human leukocyte antigen (HLA)‐B7‐restricted MN‐PND‐specific cytotoxic T lymphocytes (CTL) were also detected.Conclusions:The PPD‐MN‐PND vaccine at submicrogram doses is safe and immunogenic in PPD skin‐test‐positive healthy adult volunteers. Long lasting humoral immune responses in the serum and saliva were possibly accompanied by HLA‐B7‐restricted CTL responses. This is a vaccine prototype that can be rapidly and inexpensively modified to include other peptide epitopes. It is especially suitable for use in a worldwide multibillion Bacillus Calmette‐Guérin (BCG)‐primed or tuberculosis‐exposed population at risk for HIV‐1 infection.