OBJECTIVE: To explore the cytotoxicity to K562 cells and the solube interleukin 2 receptor (sIL 2R) level of cord blood, cord blood mononuclear cells (CBMC) activated by phytohemagglutinin (PHA), αCD3Ab and IL 2 in vitro. METHODS: By calculating the number of living cells in different culture medium systems, the proliferative capability of activated CBMC was measured. The level of sIL 2R in the supernatant of the cultured CBMC was measured using ELISA. Tumor cells necrosis induced by the effecter cells was detected by the release of 3H TdR. RESULTS: After a 3 day culture in vitro, the proliferation, cytotoxicity and the level of sIL 2R in cord blood PHA CD3AK cells were much greater than those in PHA LAK,CD3AK and LAK cells (P< 0.05 ). CONCLUSIONS: The results show that the synergistic enhancing role of PHA,IL 2 and αCD 3Ab in CBMC activation and PHA CD3AK cells have some advantages over PHA LAK, CD3AK and LAK cells in the proliferation and cytotoxicity.