In the first paper of this issue, we have described the establishment of whole platelet-captured enzyme-linked immunosorbent assay (WPC-ELISA) for the determination of platelet glycoprotein (GP) IIb/IIIa antigen. Using this method, we now analyzed the amount of GP IIb/IIIa antigen in 10 patients with Glanzmann thrombasthenia (GTA) belonging to 9 different families and their parents. In 6 patients with type I GTA who show a total lack of clot retraction, the GPIIb/IIIa antigen level ranged from 0.01% to 0.6%, and their parents (n=8) 9.3-64.9%. In 3 out of 4 patients with type II GTA who showed almost normal clot retraction indicated the level ranging from 3.6% to 5.0%, and their parents (n=4) 11.1%-35.3%. Another patient with type II GTA showed a level of 150% GPIIb/IIIa antigen, indicating that this case is a variant form of GTA.