['To analyze expression and regulation of osteopontin in human stromal endometrial and decidual cells.', 'Study by immunohistochemistry, RNase protection assay, and in vitro study.', 'Academic research unit.', 'Twenty-five fertile women.', 'Expression of osteopontin mRNA and protein was analyzed by RNase protection assay (RPA) and immunohistochemistry in secretory endometrium and decidua. Regulation of osteopontin expression in endometrial epithelial cell and stromal cells was analyzed by incubation with 17beta-estrogen, progesterone, IL-1beta, IL-6, and LIF and by incubation with cell culture supernatants of decidual natural killer cells. Furthermore, osteopontin expression was studied in stromal cells, decidualized in vitro.', 'mRNA and protein expression and regulation of endometrial stromal osteopontin.', 'Osteopontin mRNA and protein are expressed at increasing concentrations in human secretory endometrium and in decidua. High concentrations in total decidua were due to high osteopontin concentrations in decidualized stromal cells. Osteopontin mRNA and protein expression was not regulated by incubation of endometrial epithelial and stromal cells with steroids, cytokines, and natural killer cell supernatant for 6 and 24 hours. In contrast, decidualization of stromal cells for 7, 14, and 21 days resulted in significant up-regulation of osteopontin mRNA and protein.'] Is osteopontin up-regulated in human decidual stromal cells?