Color Doppler sonography is a new method that has begun to be used in the screening and early detection of ovarian malignancies. In this study the impedance to blood flow was examined by color Doppler sonography in 28 ovarian masses before exploratory laparotomy. After demonstrating the blood flow spectrum of vessels in the neovascularization area in the mass, the resistance index (Rl) was measured.Rl values were compared with the pathology reports of each mass after surgery. In five of the six malignant cases the Rl was less than 0.40 (the limit value). All of the 22 benign cases had an Rl greater than 0.40. The sensitivity and specificity of the preoperative Rl in detecting ovarian malignancy were 83 % and 100 % respectively.Our results suggest that color Doppler sonography is a useful clinical tool in the preoperative evaluation of ovarian masses.