Abstract By the preparation of platelet concentrates (PC) from buffy coat (BC) the blood component separation may be improved considerably. One can use new bag systems with bottom and top drainage (BAT) which allow partial automation of the separation procedure. Thus it is possible to produce very pure red cell concentrates (RCC) and FFP as well as BC using one separation step and well standardized conditions. Several preparative factors influence the quality of the PCs especially the storage of the whole blood and the BC. Optimal yields (0.72–0.78 × 10 11 platelets), separation efficiency (67.7–70.8%) and the lowest cell contamination (leukocytes 0.1–0.2 × 10 8, red cells 0.2–0.3 × 10 8 per concentrate) were obtained with whole blood stored for 1 h and BC for 2–4 h before resuspension by 30 min face-over-face-rotation. Because of the release of leukocyte proteases during storage, the BC should not rest for more than 2–3 h before separation of the platelets in order to prevent potential functional impairment of the platelets by proteases.