Storage of red blood cells in a nutrient-additive solution, AS-3 (Nutricel, Cutter Biological, Berkeley, CA), was evaluated after 42 and 49 days of storage by in vitro measurements of hemolysis, adenosine triphosphate (ATP) levels, glucose levels and other constituents, and in vivo study of 24-hour survival of autologous, reinfused red cells labeled with 51Cr with and without 125I human serum albumin. Two laboratories conducted the studies independently. After 42 days of storage, hemolysis was within an acceptable range (0.72 +/- 0.4% and 1 +/- 0.2%), ATP decreased to 61 percent and 56 percent in the two laboratories, and 24-hour survivals were 85.1 +/- 8.3 percent for single-label cells in one laboratory and 82.8 +/- 10 percent (single-label cells) and 84.1 +/- 13.1 percent (double-label cells) in the second laboratory. Thus, results for single- and double-label cells were similar. After 49 days of storage, ATP fell to 45 and 46 percent in the two laboratories. Twenty-four-hour recovery fell to 69.4 +/- 7.4 percent with single-label cells and to 68.2 +/- 6.7 percent with double-label cells in one laboratory. In the other laboratory, a paired study comparing AS-3 with the already approved AS-1 solution (Adsol; Fenwal Laboratories, Deerfield, IL) showed nearly identical 24-hour survivals of 71.9 +/- 8.8 percent in Nutricel and 71.8 +/- 6.5 percent in Adsol. These studies demonstrate the excellent viability of the new solution after 42 days of study. At 49 days of study, viability decreased significantly and was comparable in the two nutrient-additive solutions studied. The value of paired comparison study is demonstrated by the latter results.