Forty-two consecutive patients with advanced epithelial ovarian cancer who underwent primary surgical treatment were evaluated. The control group comprised 21 patients who had undergone surgery associated with benign pathologies. Forty-one patients had stage III disease except one who had stage IV. Optimal debulking (<1 cm) was performed in all the patients who subsequently received chemotherapy. Based on the results of the second-look laparotomy and follow-up, the patients were divided into three groups: the first group had negative second-look laparotomy or no evidence of disease during follow-up (n= 21), the second group had positive second-look laparotomy or progressive disease (n= 21), and the third was the control group (n= 21). Interleukin-12 (IL-12) levels were measured in preoperative serum and intraoperative ascites samples for all the patients. The mean serum IL-12 levels (+/-SD) in serum (S) and ascites (A) were as follows: in the first group, S: 108.44 +/- 76.40 pg/mL and A: 330.93 +/- 125.25 pg/mL; in the second group, S: 51.80 +/- 40.95 pg/mL and A: 206.89 +/- 113.47 pg/mL; and in the control group, S: 36.55 +/- 33.16 pg/mL and A: 93.62 +/- 73.07 pg/mL (P= 0.01). In the patients with advanced ovarian cancer, IL-12 levels in serum and ascites were higher compared to the levels of the controls. Also, there was an inverse relationship between initial serum and ascitic IL-12 levels and disease progression.