In patients with severe allergic reactions to plasma proteins it is possible to observe such reactions to even the small quantity of plasma contained in platelet concentrates. A platelet washing solution was designed, and platelet concentrates for four such patients were washed before infusion. Transfusion reactions were completely eliminated by the washing procedure. Platelet recovery was equivalent to that of unwashed platelets, and hemostatic effectiveness of the infused platelet concentrates was evidenced by abrupt cessation of bleeding episodes, including purpura and hematuria. Platelet washing represents a valuable, rapid and simple approach to the problem patient with thrombocytopenia and severe reactions to plasma proteins.