Objective: To assess the role of Th9 and Th17 cells in malignant ascites(MA).Methods: MA from 30 hepatic carcinoma patients and benign ascites from 30 cirrhotic patients were collected. Corresponding peripheral blood samples from these hepatic carcinoma and cirrhotic patients as well as 30 healthy subjects were collected. The frequency of Th9 and Th17 cells was tested by flow cytometry. Serum levels of interleukin(IL)-9 and IL-17 were examined by ELISA.Results: The observed frequency of Th9 and Th17 cells, and the IL-9 and IL-17 serum levels were significantly higher in MA patients than those in cirrhotic patients and healthy control samples(P < 0.05). Moreover, the Th9 cells demonstrated positive correlation with Th17 cells as well as IL-9 in MA patients; however, this positive correlation was not observed in the cirrhotic patients or healthy control samples. The frequency of Th9 and Th17 cells was distinctly higher in MA patients presenting with stage III or IV malignancy and with lymph node or distant metastasis than those in patients in stage I or II and without distant metastasis(P < 0.05).Conclusions: The increased frequency of Th9 and Th17 cells in MA patients suggests that these two T cell subsets play a synergistic role in MA pathogenesis. This study also demonstrated that Th9 and Th17 cells may perform their biological functions in conjunction with IL-9 production. Objective: To assess the role of Th9 and Th17 cells in malignant ascites (MA). Methods: MA from 30 hepatic carcinoma patients and benign ascites from 30 cirrhotic patients were collected. Corresponding peripheral blood samples from these hepatic carcinoma and cirrhotic patients as well as The frequency of Th9 and Th17 cells was tested by flow cytometry. Serum levels of interleukin (IL) -9 and IL-17 were examined by ELISA. Results: The observed frequency of Th9 and Th17 cells, and the IL-9 and IL-17 serum levels were significantly higher in MA patients than those in cirrhotic patients and healthy control samples (P <0.05). Moreover, the Th9 cells demonstrated positive correlation with Th17 cells as well as IL-9 in MA patients ; however, this positive correlation was not observed in the cirrhotic patients or healthy control samples. The frequency of Th9 and Th17 cells was distinctly higher in MA patients presenting with stage III or IV malignancy and with ly mph node or distant metastasis than those in patients in stage I or II and without distant metastasis (P <0.05) .Conclusions: The increased frequency of Th9 and Th17 cells in MA patients suggests that these two T cell subsets play a synergistic role in MA pathogenesis. This study also demonstrated that Th9 and Th17 cells may perform their biological functions in conjunction with IL-9 production.