The structure of the gamma and delta chains of the human T lymphocyte receptor has been studied extensively over the past three years. A directory of gamma/delta lymphocytes in different normal or pathological situations has been developed from the analysis of the different sub-populations of circulating (cytofluorometry) or tissue infiltrating (slice immunohistochemistry) gamma/delta T lymphocytes. It has been shown that the gamma and delta chains do not express a very polymorphic pattern; consequently, 2 or 3 anti-V or anti-V/J gamma or delta monoclonal antibodies are sufficient to evaluate any bias in the expression of this receptor in a given pathological situation. We present the genes coding for the gamma and delta chains, the proteins resulting from their expression, the different antibodies recognizing these proteins, the functions associated with gamma/delta + cells and finally certain pathological situations where an expression bias of the different gamma and delta chains has been described.