DDAVP is effective treatment in most types of von Willebrand's disease; however, in type 2B von Willebrand's disease the use of DDAVP has been contraindicated due to DDAVP-induced thrombocytopenia. Several reports have confirmed the thrombocytopenic effects of DDAVP and the presence of circulating platelet aggregates in type 2B von Willebrand's disease. We have infused three type 2B patients with DDAVP. The three patients had different mutations of their vWf. All three patients had a missense mutation which resulted in a single amino acid substitution in the disulfide loop of the A1 domain. Administration of 20 micrograms of DDAVP resulted in significant elevations of factor VIII, vWf antigen, and ristocetin cofactor levels. In contrast to other studies, DDAVP did not induce or enhance thrombocytopenia in these three patients. When blood was obtained by fingerstick and diluted into sodium oxalate (Unopette) or EDTA (Microvette), the platelet counts did not change over 4 hr. In contrast, blood collected directly into evacuated tubes containing sodium citrate, lithium heparin, or EDTA consistently demonstrated varying degrees of thrombocytopenia and platelet clumping. We also observed a shortening of the pre-infusion bleeding time over the 4 hr period. All three patients have been studied twice and each has shown consistent results. DDAVP appears to be a useful form of treatment in type 2B vWd.