BACKGROUND In preliminary studies, anaerobic red blood cell (RBC) storage reduced oxidative damage and phosphatidylserine exposure while maintaining adenosine triphosphate levels. The purpose of this study was to compare the 24-hour recovery and life span of autologous RBCs stored 6 and 9 weeks using OFAS3 additive solution in an anaerobic environment, compared to control RBCs aerobically stored in AS-3 for 6 weeks. METHODS Eight subjects were entered into a randomized, crossover study. Whole blood was collected from each subject twice separated by 12 weeks or more into CP2D and leukoreduced. Controls were stored in AS-3. Test units in OFAS3 were oxygen depleted with argon then stored 9 weeks in an anaerobic chamber at 1 to 6 degrees C. At the end of each storage period, RBCs were labeled with (51)Cr and (99m)Tc and reinfused to the subject following standard methods to determine double-label recovery and life span. Hypotheses tests were conducted using paired, repeated-measures analysis of variance. RESULTS Recovery for the anaerobically stored test RBC was significantly better than control at 6 weeks (p = 0.023). Test units at 9 weeks were not different than the 6-week control units (p = 0.73). Other in vitro measures of RBC characteristics followed the same trend. Two test units at 9 weeks had hemolysis of greater than 1 percent. CONCLUSIONS Anaerobically stored RBCs in OFAS3 have superior recovery at 6 weeks compared to the controls and equivalent recovery at 9 weeks with no change in life span. Anaerobic storage of RBCs may provide improved RBCs for transfusion at 6 weeks of storage and may enable extending storage beyond the current 42-day limit.