Matrix metalloproteinases (MMPs) are involved in many physiological and pathophysiological processes, including tumor cell invasion and metastasis. For one member of this family, MMP-13 (collagenase-3), a new, highly specific ELISA with a sensitivity of 0.5 ng MMP-13/ml was established. The protein levels of MMP-13 in ascitic fluids of 30 patients with advanced ovarian cancer FIGO stage III (n = 19) and IV (n = 11) were measured with this ELISA. Using a cut-off value of 0.5 ng MMP-13/mg total protein, two patient subpopulations with short (median 16 months) and long (median 36 months) overall survival were identified. Together with other prognostic markers, determination of MMP-13 in ascitic fluid may help to identify patients at risk for early death and help to individualize adjuvant therapy.