Platelet apheresis processing large blood volumes to produce platelet-rich plasma has become a standard procedure. In the past, platelet concentrates collected by apheresis were contaminated by large amounts of white cells. Contamination of platelet concentrates with white cells may cause typical secondary effects associated with blood transfusion as cytomegalovirus transmission, immunization to HLA class I antigens and other antigens of white cells and secretion of cytokines during storage. Therefore, a major research focus is the preparation of extremely white cell-poor platelet concentrates making additional filtration unnecessary. Apheresis procedures were developed for producing concentrates with standardized platelet content but containing almost no residual white cells. Another research interest is the evaluation of quality control-procedures detecting very low white cell-contaminations of cellular blood components. Additionally, the influence of different blood bags and of component volumes on the quality of stored platelets is examined.