Objective To investigate the expression of Th17 cells in peripheral blood of patients with sarcoidosis at different stage. Methods Flow cytometry was used to detect the Th17 cells in peripheral blood of 38 patients with sarcoidosis, including 18 cases of newly diagnosed active patients with obvious symptoms such as cough, fever, fatigue and weight loss, and 20 stable cases who were followed up regularly.15 cases of healthy volunteers were enrolled as control. Serumangiotensin-converting enzyme ( SACE) of the patients with sarcoidosis was detected by ultraviolet spectrophotometry. The cell classification and CD4 + /CD8 + T in the BALF of the newly diagnosed active patients were calculated. Results The expression of Th17 cells in peripheral blood in the patients with active sarcoidosis were higher than that in the sable patients and the controls [ ( 1. 59 ±0. 44) % vs. ( 0. 56 ±0. 32) % and ( 0. 49 ±0. 23) % , all P lt; 0. 05] . Th17 cells in peripheral blood in the patients with stable sarcoidosis and the controls were not different significantly ( P gt;0. 05) . The levels of SACE in the patients with active sarcoidosis were higher than that in the patients with stable sarcoidosis [ ( 56. 6 ±14. 6) IU/L vs. ( 35. 8 ±18. 3) IU/L, P lt; 0. 05) . There was not significant correlation between the Th17 cells in peripheral blood and SACE in the patients with sarcoidosis ( P gt;0. 05) . In the patients with active sarcoidosis, the Th17 cells in peripheral blood were not significantly correlated with lymphocyte percentages in BALF( P gt; 0. 05) , but significantly correlated with CD4 + /CD8 + in BALF ( r=0. 63, P lt;0. 05) .Conclusion In patients with active sarcoidosis, the increased expression of Th17 cells in peripheral blood may correlate with the activity of sarcoidosis.