We have previously shown that immunization with solid matrix-antigen-antibody (SMAA) complexes induces both vigorous humoral and cell-mediated immune responses and have suggested that this method of vaccination may be developed for use in humans, and potentially as a vaccine against AIDS. Here we demonstrate that a small oligopeptide can act as a tag for the construction of SMAA complexes using a tag-specific monoclonal antibody and tag-linked antigens. We show that a 14-amino acid oligopeptide, present in the phospho (P) and V proteins of simian virus 5 (SV5), retains its antigenicity when attached to the C terminus of three 'foreign' proteins [p27 and gp110 of simian immunodeficiency virus (SIV) and glutathione S-transferase] such that these proteins can be incorporated into SMAA complexes using a monoclonal antibody (MAb) that was originally raised against the native SV5 P and V proteins. Mice were immunized with SMAA complexes containing recombinant p27-TAG and MAbs have been isolated that recognized native SIV p27. The significance of these results in terms of the development of SMAA complexes as human vaccines is discussed.