Objective To explore the expression and clinical significance of CD 8 +CD28 -T lymphocytes in the patients with endometriosis ( EMT) complicating with pelvic fluid .Methods Eighty patients with endometriosis complicating with pelvic fluid ( ca-ses of ⅠtoⅣwere 15, 12, 22, and 31, respectively) were enrolled.The peripheral blood as well as the pelvic fluid were collected and flow cytometry was applied to detect the frequencies of CD 8 +CD28 -T lymphocytes and their intracellular cytokines , including transforming growth factor β1 (TGF-β1) and interleukin 10 (IL-10).Twenty health women with the same range of age were enrolled as the control group .Results Compared with the control ones , the frequencies of peripheral blood CD 8 +CD28 -T lymphocytes , TGF-β1, and IL-10 of the EMT subjects were increased significantly (all P <0.05), which presented the order Ⅳ>Ⅲ>Ⅱ>Ⅰand the difference between every two of the Ⅰ~Ⅳgroups was significant (all P <0.05).Similarly, the data of CD8 +CD28 -T lymphocytes, TGF-β1, and IL-10 in pelvic fluid also presented as Ⅳ>Ⅲ>Ⅱ>Ⅰ.Moreover, the difference of pelvic fluid TGF-β1 between any two groups was more apparent compared with CD 8 +CD28 -T lymphocytes and IL-10 ( P <0.05 ) .Spearman correlation analysis showed that any one of CD8 +CD28 -T lymphocytes, TGF-β1, and IL-10 positively correlated with any stage of ⅠtoⅣ( rs =0.791, 0.753,0.726 and all P <0.05).Conclusions CD8 +CD28 -T lymphocytes, TGF-β1, and IL-10 were closely related to the stages and could be the negative roles in the pathogenesis of EMT .TGF-β1 played a vital role in the formation of pelvic fluid .