OBJECTIVE: To study the expression of proliferative antigens in leukemic cells and the relationship between the cell proliferation activity and the prognosis. METHODS: The labeling index (LI) of CD71, Ki-67 and PCNA in normal and leukemic cells were measured by flow cytometry. RESULTS: In normal children, the LI of CD71, Ki-67 and PCNA was (32.18 +/- 16.66)%, (4.82 +/- 9.27)% and (19.69 +/- 25.11)%, respectively, while in ALL children, which was (33.66 +/- 21.52)%, (32.14 +/- 23.59)% and (47.46 +/- 30.96)%, respectively. The PCNA LI of leukemia cells was (47.46 +/- 30.96)% and (27.28 +/- 12.51)% when patients was at presentation and remitted for 3 years, respectively, and was (52.59 +/- 32.00)% and at presentation in 28 CCR children and and (26.94 +/- 14.48)% in 7 high-risk group ALL children (F = 8.877, P < 0.01), respectively. CONCLUSIONS: The proliferation, LI of leukemic cells was higher than that of normal cells, and reduced to normal level after treatment. The higher PCNA proliferation of untreated cells was a favourable marker for prognosis.