A product of growth arrest-specific gene 6 (Gas6) is known to be synthesized by growth-arrested cells. In this study, we found that several rat tissues including platelets contain Gas6 and activation of the platelets with thrombin provoked the release of Gas6. ADP and collagen, which as well as thrombin stimulated release of ATP from platelets, also enhanced the release of Gas6, suggesting that the mechanism of its release was similar to that of ATP release. This study provides the first evidence of growth arrest-independent secretion of Gas6 and suggests the involvement of Gas6 in vascular diseases as well as hemostasis.