Great amounts of haematopoietic stem cells can be collected after conditioning with growth factors and myelosuppressive treatment. With the immunadsorption technique (Ceprate SC(R)) CD34+ cells can be purified and concentrated with an overall loss of about 20-40%. Retransfusion of CD34+ purified cells resulted in a rapid and sustained engraftment after myeloablative treatment. Thus CD34+ selection by immunadsorption offers the opportunity to purify stem cells concentrates from platelets, red cells and granulocytes and to minimize DMSO toxicity.