BACKGROUND: Cytokines play a key role in the regulation of cells of the immune system and also have been implicated in the pathogenesis of malignant disease. Usually malignant cells secreted various types of cytokine, and the cytokine levels have been shown to be potential for diagnosis of malignant disease. To differentiate the ovarian cancer from other benign diseases, the levels of cytokine in peritoneal fluid have been revealed more effect than those in blood. METHODS: The levels of interferon-gamma, tumor necrosis factor-alpha, interleukin-1 beta, interleukin-5, interleukin-6 and interleukin-10 in peritoneal fluid from 31 cases of ovarian cyst, 14 cases of ovarian cancer, and 20 cases of endometriosis were determined by enzyme-linked immunosorbent assay(Endogen Inc., USA). RESULTS: The mean level of interleukin-1 beta, interleukin-6, and interleukin-10 in the patients of in ovarian cancer were 10.49+/-17.44 pg/mL, 705.79+/-236.06 pg/mL and 231.56+/-145.43 pg/mL, respectively, which were significantly higher than in ovarian cyst(2.00+/-2.04 pg/mL, 103.42+/-154.49 pg/mL and 27.90+/-23.20 pg/mL, respectively)(P<0.05). The mean concentration of interferon-gamma, tumor necrosis factor-alpha, and interleukin-5 in patients of ovarian cancer were not significantly different from the benign group. CONCLUSIONS: The cytokine levels of peritoneal fluid in ovarian cancer were significantly higher than ovarian cyst and endometriosis. So, the measurement of cytokine level in neoplastic effusion could be useful to differentiate malignant from ovarian cyst.