The recombinant fragment of the platelet membrane glycoprotein Ia/IIa (rGPIa/IIa) was conjugated to the polymerized albumin particles (polyAlb) with the average diameter of 180 nm. The intravenous administration of rGPIa/IIa polyAlb to thrombocytopenic mice ([platelet] = 2.1 +/- 0.3 x 10(5) particles/muL) with three doses of ca. 2.4 x 10(10), 7.2 x 10(10), and 2.4 x 10(11) particles/kg, respectively, significantly reduced their bleeding time to 426 +/- 71, 378 +/- 101, and 337 +/- 46 s, respectively, whereas that of the control groups (PBS) was 730 +/- 198 s. The injection of rGPIa/IIa-polyAlb (2.4 x 10(11) particles/kg) was approximately equal to the effect of the injection of the mouse platelets at a dose of 2.0 x 10(10) particles/kg. It was confirmed that rGPIa/IIa-polyAlb had a recognition ability against collagen and could contribute to the hemostasis in the thrombocytopenic mice as a platelet, substitute. (C) 2003 Elsevier Science (USA). All rights reserved.