This study was purposed to investigate the immune state of T cells, the quantity and function of GPI(+) T cells and GPI(-) T cells in patients with paroxysmal nocturnal hemoglobinuria (PNH). 22 cases of PNH and 18 normal controls were enrolled in this study. Their T lymphocyte subsets, Th lymphocyte subsets were assayed by flow cytometry with the monoclonal antibodies concerned. The proportion of GPI(+) T cells or GPI(-) T cells in CD3(+) T cells, CD4(+) T cells, CD8(+) T cells and the expressions of CD69 on these T cells were also respectively assayed. The results showed that the proportion of CD4(+) T cells in CD3(+) T cells in PNH [(47.7670 +/- 13.91139)%] was lower than that in controls [(54.9592 +/- 7.11678)%] (p < 0.05). CD8(+) T cells in CD3(+) T cells of PNH cases [(52.2767 +/- 13.90395)%] were higher than that of controls [(45.2418 +/- 6.75306)%] (p < 0.05). The ratio of CD4(+) T cells to CD8(+) T cells was reverse in PNH. Those were more significantly in PNH-AA (0.77763 +/- 0.409153) (p < 0.05). The proportion of Th1 cells in PNH [(16.9136 +/- 6.78899)%], especially in PNH-AA [(22.8000 +/- 5.45244)%], was significantly higher than that in controls [(4.4600 +/- 1.81879)%] (p < 0.05). The proportion of Th2 cells in PNH [(4.7582 +/- 1.98441)%] had no difference from controls [(3.7960 +/- 1.13810)%]. The number of GPI(-) T cells in CD8(+) T cells and CD4(+) T cells were (14.6797 +/- 11.96718)% and (3.9241 +/- 2.46263)% respectively. The expression of CD69 on GPI(+) T cells or GPI(-) T cells in PNH [CD8(+) GPI(+) T cells (17.67881 +/- 8.562493)%, CD8(+) GPI(-) T cells (15.86575 +/- 7.279743)%, CD4(+) GPI(+) T cells (4.65431 +/- 1.984378)%, CD4(+) GPI(-) T cells (4.93181 +/- 1.730001)%]was significantly higher than that in normal controls [CD8(+) GPI(+) T cells (4.68038 +/- 1.216645)%, CD4(+) GPI(-) T cells (1.77339 +/- 0.645259)%] (p < 0.05), but the expression of CD69 on GPI(+) T cells was not different from that on GPI(-) T cells in PNH. It is concluded that high function of cytoimmunity in PNH may be responsible for bone marrow failure but not relates to the existence of PNH clone in T cell population.