We investigated menstrual cycle-dependent changes in the expression of PTHrP and PTH/PTHrP receptor in the human endometrium by immunohistochemistry, and competitive reverse transcription and polymerase chain reaction (RT-PCR). Human endometrial tissues were obtained from patients who underwent gynecological surgery due to cervical cancer (carcinoma in situ) or ovarian cancer. The mean age of the 20 patients was 36.5 (range 31-44) years. For analysis of mRNA expression, specimens from proliferative (mid, n=5; late, n=5) and secretory (early, n=4; mid, n=4) phases were used. Immunohistochemical expression of PTHrP and PTH/PTHrP receptor was observed in the cytoplasm of both epithelial and stromal cells. Stronger staining of PTHrP was found in glandular epithelial cells than in stromal cells. The staining during the proliferative phase was stronger than that in the secretory phase and the difference was particularly remarkable when comparing samples from the same patient. PTH/PTHrP receptor was also present in both epithelial and stromal cells of the endometrium. However, no difference was observed in receptor expression between the proliferative and secretory phases. Competitive RT-PCR revealed that the expression of PTHrP mRNA was higher during the proliferative phase than in the secretory phase, although no difference was observed in PTH/PTHrP receptor mRNA expression. The data suggest that endometrial proliferation may be mediated by a local PTHrP autocrine and/or paracrine mechanism.