Soft and hard-packed red blood cells in four different CPD anticoagulant-preservative solutions were stored with and without added glucose, adenine, and electrolytes. The hemoglobin-oxygen affinity of the red blood cell concentrates was tested over a six-week storage period. No single solution conferred better protection than any other against an expected increase in oxygen affinity due to loss of 2,3-DPG during storage. In all solutions, P50 at pH 7.4 decreased linearly when measured in a physiological system using CO2. After six weeks' storage at 4 C, the normal oxygen-binding properties of red blood cells could be restored in all instances following incubation for one hour in a rejuvenation solution. By contrast, red blood cell ATP levels were highest when resuspending solutions contained adenine and added glucose, but did not significantly compensate the allosteric role of 2,3-DPG in regulating oxygen affinity when the latter became depleted.