We reported a 33-year-old woman with thrombasthenia (type II) in whom 1-deamino-8-D-arginine vasopressin (DDAVP) was available for the hemostasis control during breast tumor resection. She has had recurrent nasal bleeding and purpura since 2 years old. On the first admission to our hospital because of hematuria at 18 years old, she was diagnosed as thrombasthenia (type II) from hemostatic studies. At 20 years old, she had a healthy baby by the cesarean section with transfusion of fresh blood and platelet concentrates. On the 5th admission for the breast tumor resection, defect of glycoprotein II b-III a of her platelets was confirmed by using SDS gel electrophoresis. Recently, there are some reports on availability of DDAVP for hemostatic control in platelet dysfunction of various etiologies as well as mild hemophilia and von Willebrand disease. So, DDAVP (0.4 microgram/kg) was used for hemostasis control. After 1 hour, the bleeding time was shortened from over 10 to 4 min, platelet adhesiveness to glass beads increased from 1.8 to 37%. Furthermore, the levels of Ristocetin cofactor and von Willebrand factor antigen (especially large multimer) also increased. But platelet aggregation with various inducers remained unchanged before and after infusion. Breast tumor (fibroadenoma) resection.