The integrin alphaIIb beta3 is a membrane receptor which was considered to be expressed only in cells of megakaryocytic lineage. We have shown that alphaIIb beta3 is expressed in mouse melanoma B16a cells, and in human prostate adenocarcinoma cells. The purpose of this study was to determine whether the megakaryocytic product alphaIIb beta3 was functionally expressed in other non-megakaryocyte lineage tumor cells. By using the reverse transcription polymerase chain reaction (RT-PCR), we have obtained data demonstrating that alphaIIb beta3 is expressed in a variety of tumor cell lines (17) derived from different species (human, rat and mouse) and of different histological origins (skin, blood, lung, liver, kidney, cervix, colon, bladder, breast and prostate). Immunostaining of tumor cells with a monoclonal antibody (MAb) to alphaIIb beta3 demonstrates that alphaIIb beta3 protein is also expressed in tumor cells. A protein kinase C activator PMA stimulates adhesion of tumor cells to fibronectin and fibrinogen, and this stimulated adhesion is blocked by a function-blocking MAb directed to alphaIIb beta3. Our results indicate that the megakaryocytic gene product alphaIIb beta3 integrin is widely expressed among tumor cells of non-megakaryocytic lineage, suggesting that ectopic expression of this integrin may play an important role in tumor progression.