Calcified psammoma bodies often appear in human ovarian serous papillary cystadenocarcinoma. Osteocalcin (OC), osteonectin (ON) and osteopontin (OPN) are three members of non-collagenous bone-related proteins known to be related with mineralization of bone. To clarify possible involvement of these bone matrix proteins in the calcification of the psammoma bodies, the expression of OC, ON and OPN was analyzed by immunohistochemical and in situ hybridization studies using 15 surgical specimens. OPN protein was detected in the calcified area of the psammoma bodies which was positively stained by von Kóssa's staining, while OC and ON proteins were not. OPN protein was not detected in any cells in tissues, but OPN messenger ribonucleic acid (mRNA) was detected in CD68-positive macrophages, indicating that OPN was produced and promptly secreted by macrophages. These results suggest that OPN produced and promptly secreted by macrophages and subsequently translocated to psammoma bodies may be causally related with the calcium phosphate deposition in the psammoma bodies of the ovarian serous papillary cystadenocarcinomas.