The heat shock protein, Hsp 70, has been shown to play an important role in tumour immunity. Vaccination with Hsp 70-peptide complexes (Hsp70-PCs), isolated from autologous tumour cells, can induce protective immune responses. We have developed a novel method to identify synthetic mimic peptides of Hsp70-PCs and to test their ability to activate T-cells. Peptides (referred to as "recognisers") that bind to Hsp70-PCs from the human breast carcinoma cell line, MDA-MB-231, were identified by bio-panning a random peptide M13 phage display library. Synthetic recogniser peptides were subsequently used as bait in a reverse bio-panning experiment to identify potential Hsp70-Pc mimic peptides. The ability of the recogniser and mimic peptides to prime human lymphocyte responses against tumour cell antigens was tested by simulating lymphocytes with autologous peptide-loaded monocyte-derived dentritic cells (DCs). Priming and subsequent stimulation with either the recogniser or mimic peptide resulted in interferon-y (IFN-y) secretion by the lymphocytes. Further more, DCs loaded with Hsp70-PC or the recogniser or the mimic peptide primed the lymphocytes to respond to soluble extracts from breast cells. These results highlight the potential application of synthetic peptide-mimics of Hsp70-PCs, as modulators of the immune response against tumours.