Red cell concentrates with hematocrit values of 80 +/- 5 percent were stored at 4 degrees C either in citrate-phosphate-dextrose for 22 to 28 days or in citrate-phosphate-dextrose-adenine-one for 35 to 39 days. After storage, the red cells had reduced 2,3-diphosphoglycerate and adenosine triphosphate levels, and biochemical treatment with a solution called PIPA was used to restore these levels. The red cells were not preserved further, but instead were washed after rejuvenation with an unbuffered sodium chloride-glucose solution, pH 5.0, for in vivo studies, and with a buffered sodium chloride-glucose-phosphate solution, pH 6.8, for comparative in vitro studies. The red cells were stored in the wash solution at 4 degrees C for 72 hours after washing. Red cell recovery after washing was about 95 percent. Twenty-four-hour posttransfusion survival value was about 80 percent, and the index of therapeutic effectiveness was greater than 75 percent. These biochemically modified washed red cells exhibited higher than normal P50 values, even after 3 days of postwash storage at 4 degrees C. The units that were washed with the sodium chloride-glucose solution with a pH of 5.0 exhibited a greater degree of hemolysis after 3 days of postwash storage at 4 degrees C than did the units that were washed with the sodium chloride-glucose-phosphate solution with a pH of 6.8.(ABSTRACT TRUNCATED AT 250 WORDS)