Uremia causes a bleeding tendency associated with platelet dysfunction, and previous studies have shown abnormalities of platelet glycoprotein (GP) lb or GPIIb/IIIa and a tendency for platelet activation in uremia. The present study compared the abnormalities of platelet function in uremia with (n=l) or without (n=18) associated Glanzmann’s thrombasthenia. There was a significant difference between ristocetin-induced agglutination of platelets from the uremic patients without Glanzmann’s thrombasthenia and platelets from healthy controls (n = 15). In addition, a reduction of GPIb expression by uremic platelets along with normal GPIIb/IIIa expression was confirmed using flow cytometry. Many coagulation markers were increased in the uremic patient with Glanzmann’s thrombasthenia, suggesting that the coagulation was enhanced and the platelets were prone to activation. However, the thrombasthenic platelets actually showed little increase in the binding of a monoclonal anti-CD63 antibody directed against lysosomal integral membrane protein (which is expressed after platelet activation), while uremic platelets showed a marked increase. In addition, the expression of GPIb by thrombasthenic platelets was normal, while that of GPIIb/IIIa was markedly decreased. Our results suggest that thrombasthenic platelets are resistant to activation and to the degradation of GPIb under uremic condition and that this difference from ‘ordinary’ uremic platelets be related to the difference in G