A possible role of the peptide binding protein (PBP) 72/74 in antigen processing and presentation has been recently suggested in mice. In order to evaluate a possible analogous role of a PBP72/74-related protein in humans, immunoelectron microscope investigations, functional studies, and immunofluorescence analyses were performed on normal human peripheral antigen-presenting cells. We demonstrated that the determinant recognized by antiheat shock protein (HSP) 72/73 monoclonal antibody (MoAb) is constitutively expressed on the cell surface of monocytes as well as of B cells. Moreover, the capability of monocytes to present a recall antigen to T cells was significantly decreased when preincubated with an anti-HSP72/73 MoAb. These data add further strength to a potential role of a protein related to human PBP72/74 homologue in antigen processing and/or presentation. Finally, the capability of anti-HSP72/73 MoAb to impair the ability of fixed monocytes to present a synthetic peptide demonstrates that cell surface- localized PBP72/74-related protein could play a role in antigen presentation.