The expression of neutrophil gelatinase-associated lipocalin (NGAL) has been shown to be upregulated in ovarian cancer cells. In this study, we report that the expression of immunoreactive NGAL (irNGAL) in ovarian tumors changes with disease grade and that this change is reflected in the concentration of NGAL in peripheral blood. A total of 59 ovarian tissues including normal, benign, borderline malignant and grades 1, 2 and 3 malignant were analyzed using immunohistochemistry. irNGAL was not present in normal ovaries and the NGAL expression was weak to moderate in benign tissues. Both borderline and grade 1 tumors displayed the highest amount of NGAL expression with moderate to strong staining, whereas in grade 2 and 3 tumors, the extent of staining was significantly less (p < 0.01) and staining intensity was weak to moderate. Staining in all cases was confined to the epithelium. NGAL expression was analyzed by ELISA in 62 serum specimens from normal and different grades of cancer patients. Compared to control samples, the NGAL concentration was 2 and 2.6-fold higher in the serum of patients with benign tumors and cancer patients with grade 1 tumors (p < 0.05) and that result was consistent with the expression of NGAL performed by Western blot. NGAL expression was evaluated by Western blot in an immortalized normal ovarian cell line (IOSE29) as well as ovarian cancer cell lines. Moderate to strong expression of NGAL was observed in epithelial ovarian cancer cell lines SKOV3 and OVCA433 while no expression of NGAL was evident in normal IOSE29 and mesenchyme-like OVHS1, PEO.36 and HEY cell lines. NGAL expression was downregulated in ovarian cancer cell lines undergoing epithelio-mesenchymal transition (EMT) induced by epidermal growth factor (EGF). Downregulation of NGAL expression correlated with the upregulation of vimentin expression, enhanced cell dispersion and downregulation of E-cadherin expression, some of the hallmarks of EMT. EGF-induced EMT phenotypes were inhibited in the presence of AG1478, an inhibitor of EGF receptor tyrosine kinase activity. These data indicate that NGAL may be a good marker to monitor changes of benign to premalignant and malignant ovarian tumors and that the molecule may be involved in the progression of epithelial ovarian malignancies.