An improved method for separating whole blood into components and collecting adesired blood component. The method allows a desired blood component to besubjected tocentrifugal forces within a separator for prolonged periods of time, yieldinga cleaner cut andhigher yield of the desired blood component. Whole blood is drawn from asource andpumped into a separator, the undesired blood components are removed from theseparator atrates so as to build up the desired blood component in the separator. Thedesired bloodcomponent is only removed after a predetermined amount of the desired bloodcomponenthas built up in the separator. It is preferred that the desired bloodcomponent be buffy coatand that the method be used to perform photopheresis treatments. In anotheraspect, theinvention is a method of performing a full photopheresis treatment to treatdiseases in areduced time, preferably less than about 70 minutes, and more preferably lessthan about 45minutes.
