The human granzyme B gene encodes a serine protease expressed specifically in cytoplasmic granules of cytotoxic T lymphocytes, released upon effector-target cell interaction. Previous studies have shown that granzyme B mRNA was induced in T lymphocytes after antigenic or mitogenic stimulation. To study the regulation of human granzyme B gene expression during lymphocyte activation we analyzed its 5' flanking region using chloramphenicol acetyl transferase (CAT) reporter gene constructs. We show that a 208-bp fragment (-148 to +60) containing an NF-AT (nuclear factor of activated T cells)-binding site promotes CAT expression in phytohemagglutinin-activated T lymphocytes, in immobilized monoclonal anti-CD3 antibody-activated Jurkat T cell line while it is inactive in unstimulated PEER and Jurkat T cells lines or B Epstein-Barr virus-transformed cell lines.