Transplantation of hematopoietic stem cells shortens the pancytopenic period after chemotherapy. In the time between harvest of hematopoietic cells and retransfusion the graft is usually preserved by cryoconservation. Preservation requires the use of cryoprotectants such as DMSO resulting in a loss of a large number of viable CD34+ cells in the transplant. Therefore, we developed an automated and completely closed, hollow-fiber membrane based system for the conservation of stem cells covering the time period of most of the high-dose chemotherapeutic regimens. 125 ml buffy coat preparation of normal donors (RBC: 5,4±0,3 x 10e6/µl, WBC:21,0±5,0 x10e3/µl, n=3, mean ± SD) used as a model for mobilized blood were kept in the system at room temperature. The system allows long-term anticoagulation, continuous supply with nutrients and removal of waste products resulting in strictly controlled pH- and p02-levels. Sedimentation of blood cells was avoided by continuous blood flow and mixing. In conclusion, Cytocare is a newly developed, closed and automated system for the conservation of hematopoietic stem cells in whole blood. The use of the toxic cryoprotectant DMSO can be avoided which is an advantage for grafts with a low count of CD34+ cells. The high flexibility of this system allows processing of blood volumes from 50 ml (for cord blood) up to 1000 ml.