Integrins are a family of cell surface molecules that mediate the attachment of cells to the extracellular matrix (ECM). These alphabeta heterodimers are involved in many biological processes. We used northern blotting and in situ hybridization to study the pattern of beta3 integrin gene expression during mouse embryogenesis. Northern blotting detected two species of beta3 mRNA from 7 to 17 days post coitum (dpc). These transcripts were abundant in the adult testis, kidney, liver, spleen, and heart. In situ hybridization experiments detected high levels of beta3 in the major haematopoietic and lymphoid organs: yolk sac, liver, and thymus. Moreover, beta3 transcripts were also detected in the vascular system, where beta3 integrin probably plays a key role in angiogenesis and vasculogenesis. We also detected a hybridization signal in the gut, the bronchioles of the lungs, and the bladder wall. beta3 transcripts were also present in the medullary regions of the adrenal glands and in the developing skeleton. Our study shows that beta3 gene expression is not restricted to the liver and gut during mouse development. We also detected beta3 integrin mRNA in the yolk sac, vessels, lung, bladder, and developing bones. Our data suggest that beta3 integrin plays a key role in many important physiological processes like haematopoiesis, angiogenesis, phagocytosis, and bone resorption.