The characteristics of previously frozen red blood cells, prepared in a large-scale frozen blood program using the Red Cross method were evaluated. The use of the method as originally described resulted in approximately 91 per cent freeze-thaw-wash recovery of red blood cells. When the glycerolization step was modified by adding the partially glycerolized erythrocytes into 300 ml of 6.2M glycerol, freeze-thaw-wash recoveries were decreased. However, gradient addition of glycerol to the red blood cells without the use of stylet, resulted in acceptable in vitro recoveries. Thawing frozen units in waterbath, to which no antiseptic was added, could introduce bacteria into units of previously frozen red blood cells. Therefore, it seems advisable to use dry heat thawing procedures. Previously frozen red blood cells prepared in the large scale maintained normal levels of ATP and 2,3 DPG. Therapeutic transfusions had acceptable 24-hour survival in vivo.