We compared the rapidity of rewarming and infusing red blood cells (RBCs) mixed with 24°C, 50°C, and 60°C saline with the rapidity of administering undiluted RBCs through a heat exchanger. We measured flow rate, final temperature, and hemolysis in matched 41–45-day-old pooled AS-1 RBCs infused through high-flow tubing via a 14-gauge catheter under the influence of gravity. Undiluted RBCs were tested as controls. The final temperature of the 60°C admixture technique was lower than that with the heat exchanger (28.5 ± 0.2°C vs. 32.7 ± 0.2°C), but the flow rate was higher (258 ± 8 mL/min vs. 61 ± 4 mL/min). Admixture with 60°C saline resulted in no increase in hemolysis. This technique appears to be a simple, inexpensive method for rapid rewarming and infusion of RBCs and may be valuable for administration of RBCs simultaneously through multiple sites during resuscitation.