The aim of this study was to evaluate the expression of ZAP70 changing during disease progression, the intracellular interferon gamma (IFN-γ) and IL-4 content of T and B lymphocytes and the CLL cell subset (CD5+CD19+) in CLL patients and healthy subjects, and ZAP70 correlation with cytokine production. The gene discussed is ZAP70; the disease is B-cell chronic lymphocytic leukemia.