Using 70% 24‐hour posttransfusion survival as one of the criteria of preservation, ACD and CPD anticoagulant solutions with and without adenine were tested after storage for 28, 35, or 42 days. At 28 days, all solutions had average survivals of 70% or better. The average survival values for the ACD and CPD solution groups were less than 70% at 35 and 42 days. However, both solutions with adenine had a group average value over 70% even after 35 or 42 days of storage. The average survival values between the two anticoagulants alone, were not significantly different at each time period. The two anticoagulants when adenine was included had increased survival and there was no statistical difference between the levels. In comparing two units obtained from the same subject, survival percentages were significantly higher in almost every recipient when the adenine‐supplemented stored blood was used. Other chemical determinations did not show significant alterations and no toxic effects were observed in the recipients.Since all units containing adenine had survival values greater than 70% in the 28‐ and 35‐day periods, these units would appear to have been effectively preserved and blood stored under these conditions could be used in routine transfusions, reserving units stored 42 days for emerge