During intensive treatment of haemoblastoses it is important to administer repeatedly high-quality platelet concentrates. The authors describe the first results obtained with the use of an isoradial chamber of Travenol Co. for separation on a CS-3000 separator. Using the chamber, they achieved in the first 20 patients a reduction of the separation time by 30 mins. (23%) and the thrombocyte yield was not reduced. The resulting product contained, however, more leucocytes. The chamber can be used to reduce the separation period also under Czechoslovak conditions where donors have smaller numbers of thrombocytes than reported by western authors (the microcomputer of the separator is set for a regime suited for larger thrombocyte numbers).