A putative tumor suppressor, PTEN/MMAC1 gene was recently identified at 10q23 and was found to be frequently altered in several types of human tumors. To determine the possible role of this gene in human ovarian tumors, we screened 31 unselected primary epithelial ovarian cancers with matched normal tissues and 7 ovarian cancer cell lines. Two homozygous deletions (4.8%) were detected in primary ovarian tumors by a semi-quantitative multiplex polymerase chain reaction. However, no point mutations were observed in any of the PTEN/MMAC1 coding sequences as determined by denaturing high-performance liquid chromatography and DNA sequencing. These data indicate that PTEN/MMAC1 mutations are rare in ovarian cancers.