Collection of mononuclear cells and peripheral blood stem cells

A method for collecting mononuclear cells, comprising:

• separating blood in a separation chamber into a red blood cell layer, a plasma constituent, and a mononuclear cell-containing layer;
• conveying a portion of the plasma constituent from the separation chamber via a plasma outlet and conveying a first portion of the red blood cell layer from the separation chamber via a red blood cell outlet while allowing a volume of the mononuclear cell-containing layer to increase in the separation chamber;
• conveying a second portion of the red blood cell layer from the separation chamber via the red blood cell outlet to a red blood cell collection container;
• conveying at least a portion of the contents of the red blood cell collection container to the separation chamber to convey at least a portion of the mononuclear cell-containing layer out of the separation chamber for collection;
• and
• conveying plasma from the separation chamber via the plasma outlet to more fully collect said at least a portion of the mononuclear cell-containing layer without the use of collected plasma.