ZAP-70 is a 70 kD protein tyrosine kinase associated with the zeta chain of the T cell receptor. It is expressed in T cells and NK cells and has been shown to be involved in T cell signaling. Defects in ZAP-70 have been linked to selective T cell defects. The ZAP-70 kinase undergoes multiple phosphorylation events after T cell receptor engagement and interacts with a number of proteins involved in signal transduction. Recently, ZAP-70 has been identified as an important prognostic marker in B-cell chronic lymphocytic leukemia (B-CLL). The 1E7.2 monoclonal antibody recognizes human and mouse ZAP-70 and has been shown to be useful for flow cytometry, Western blotting, and immunoprecipitation.