To study the effects of S-2-(3-aminopropylamino) ethyl phosphorothioic acid (WR-2721, amifostine) on proliferation inhibition and apoptosis of HL-60 human leukemia cell line, the cell apoptosis rate of HL-60 was determined by annexin V/PI double staining method. Cell proliferation and chemotherapy sensitivity were analyzed with XTT assay, and the changes of cell cycle were observed through flow cytometry. The results showed that WR-2721 could significantly inhibit HL-60 cell proliferation. After treatment (30 min, 37 degrees C) with WR-2721, the sensitivity of HL-60 cells to VP16 was enhanced, and the IC(50) descended from 52.5 micro g/ml to 40.5 microg/ml. After 72 hours treatment of HL-60 cells with WR-2721, the early apoptotic cells (annexin V-FITC positive/PI negative) were increased from (5.5 +/- 1.9)% to (48.5 +/- 8.4)% (P < 0.001), late apoptotic cells (annexin V-FITC positive/PI positive) were increased from (1.2 +/- 0.5)% to (39.0 +/- 4.0)% (P < 0.001), and HL-60 cells were arrested in G(2)-M phase. In conclusion, WR-2721 treatment can enhance HL-60 cell chemotherapy sensitivity to VP16, inhibit proliferation, induce apoptosis and accumulation of cells in G(2)-M phase.