An anti-idiotypic monoclonal antibody 2A9 (Ab2) was prepared, which mimicked the nasopharynegeal carcinoma (NPC) cell antigen defined by anti-NPC McAb Fcl. The abilities of 2A9's inducing humoral and cellular immunity against NPC cell antigen were studied in syngeneic mice by inducing anti-Ab2 sera (Ab3) and delayed-type hypersensitivity. Two periods of phase I clinical trials were carried out, stage IV NPC patients receiving radiotherapy were chosen. Human anti-mouse antibodies (HAMA), anti-anti-idiotypic antibodies (Ab3), and anti-NPC cell antibodies (Abl') were detected by ELISA. TNF-obiL-2, IFN- T levels in sera were determined by ELISA Kits. IL-2 mRNA expression in peripheral blood mononuclear cells (PBMC) were shown by in situ hybridization. The results showed that 2A9 was safe in applying on NPC patients and induced some humoral and/or cellular immune responses.