To study the expression of tankyrase (a positive regulator of telomerase activity) in malignant hematopoietic cells and its relation with telomerase activity, the method of realtime quantitative PCR with fluorescence probe hybridization were used to measure expression of tankyrase and hTERT in myeloid leukemia cell lines K562, HL-60, U937, NB4, THP-1, HEL, Dami and T lymphocytic leukemia cell lines 6T-CEM, Jurkat and B-cell lymphoma cell line Raji. CD3(+), CD19(+) and CD33(+) cells separated from normal human mobilized peripheral blood by immunomagnetic bead system and 10 mononuclear cell samples separated from bone marrow of normal individuals were served as normal controls. The results indicated that the expression of tankyrase in malignant hematopoietic cell lines was significantly higher than that in normal controls (U = 19, P < 0.01). Its expression in myeloid leukemia cell lines is higher than in normal CD33(+) cells, the expression in T lymphocytic leukemia and B-cell lymphoma cell lines is higher than in CD3(+) and CD19(+) cells respectively. Its expression in myeloid malignant hematopoietic cell lines is significantly lower than in lymphocytic ones (0.0032 +/- 0.0010 vs. 0.012 +/- 0.0016, F = 23, P < 0.01). The expression of tankyrase correlated positively with hTERT (Spearman correlation coefficient is 0.395, P < 0.05). It is concluded that tankyrase is overexpressed in malignant hematopoietic cell lines, that may be one of the causes of high-produced telomerase activity in malignant hematopoietic diseases.