A sample was submitted for serologic evaluation from a pregnant patient with immune thrombocytopenic purpura (ITP) for possible transfusion in the future because of a decreased platelet count. Anti-D and -E were identified in the patient’s serum using several antibody identification techniques, and anti-D was recovered in an acid eluate prepared from the patient’s red cells. It was discovered that WinRho™ had been administered to treat the ITP. This product has been licensed for treatment of nonsplenectomized D+ children and adults with ITP to increase the platelet count. Administration of anti-D to D+ individuals for treatment of ITP can cause a red cell anemia.