Platelet membrane glycoproteins play important roles in platelet functions. In this symposium, we reported three types of deficiency of platelet membrane glycoproteins; Glanzmann's thrombasthenia, Bernard-Soulier syndrome, GPIV-deficiency and discussed the roles of GPIIb/IIIa, GPIb and GPIV, respectively, in the aggregation of these abnormal platelets. In a patient with Bernard-Soulier syndrome, the abnormality in the patient's GPIb was caused by the double heterozygote from her parents who were unrelated. Roles of GPIV were negligible in platelet aggregation since the GPIV-deficient platelets (Naka-) found in healthy donors showed normal platelet aggregations. We developed two monoclonal antibodies, TM83 and TM60 against GPIIIa and GPIb, respectively, and showed that these antibodies inhibited the function of GPIb and GPIIb/IIIa complex, respectively. We demonstrated that TM83 inhibited an epitope of GPIIIa and/or GPIIb/IIIa complex which changes its conformation due to Ca2+ deprivation and is essential for exposure of the fibrinogen-binding site.