Tetrandrine, a bisbenzylisoquinoline alkaloid, was found to cause death of malignant lymphoid and myeloid cells but not of Epstein-Barr virus-transformed lymphoblastoid cells. The death took the form of apoptosis (programmed cell death), the nature of the process being confirmed by DNA gel electrophoresis and electron microscopy. The induction of apoptosis by tetrandrine was much more rapid in CEM-C7 cells (4 h) than in the same cells treated with glucocorticoids (40 h), and did not require de novo protein synthesis. These results suggest that the anti-inflammatory and immunosuppressive properties of tetrandrine are mediated by novel mechanisms worthy of further investigation. They also indicate that tetrandrine may have value as an anti-neoplastic agent.