The ability of T-cell receptor (TCR) γδ cells to recognize foreign non-peptide antigens suggests a role in mucosal surveillance. However, their expansion, together with the presence of antigen-presenting cells (APCs) expressing CD1 antigens (a ligand for γδ TCRs), in the respiratory tract of allergic subjects also suggests a pathogenic role for these cells in allergic diseases. Here, the hypothesis is presented that γδ T cells and CD1 + APCs may operationally distinguish healthy from atopic status.