The peroxisome proliferator-activated receptors (PPARs) belong to a subclass of nuclear hormone receptor that executes important cellular transcriptional functions. Previous studies have demonstrated the expression of PPARgamma in several tumours including colon, breast, bladder, prostate, lung and stomach. This study demonstrates the relative expression of PPARgamma in normal ovaries and different pathological grades of ovarian tumours of serous, mucinous, endometrioid, clear cell and mixed subtypes. A total of 56 ovarian specimens including 10 normal, eight benign, 10 borderline, seven grade 1, nine grade 2 and 12 grade 3 were analysed using immunohistochemistry. Immunoreactive PPARgamma was not expressed in normal ovaries. Out of eight benign and 10 borderline tumours, only one tumour in each group showed weak cytoplasmic PPARgamma expression. In contrast, 26 out of 28 carcinomas studied were positive for PPARgamma expression with staining confined to cytoplasmic and nuclear regions. An altered staining pattern of PPARgamma was observed in high-grade ovarian tumours with PPARgamma being mostly localized in the nuclei with little cytoplasmic immunoreactivity. On the other hand, predominant cytoplasmic staining was observed in lower-grade tumours. Significantly increased PPARgamma immunoreactivity was observed in malignant ovarian tumours (grade 1, 2 and 3) compared to benign and borderline tumours (chi2 = 48.80, P < 0.001). Western blot analyses showed significant elevation in the expression of immunoreactive PPARgamma in grade 3 ovarian tumours compared with that of normal ovaries and benign ovarian tumours (P < 0.01). These findings suggest an involvement of PPARgamma in the onset and development of ovarian carcinoma and provide an insight into the regulation of this molecule in the progression of the disease.