In the operation room of S.N.U.H., 10 patients were transfused with A,C.D. stored blood after warming to 36 degrees C by using a blood warmer. Observed changes of Na+, Cl-, K+ and. Ca++ were as follows. 1) Before warming, the electrolytes of A.C.D. stored blood were Na+ 148. 2 mEq/1, Cl-; 117. 0 mEq/1 and K+; 8. 4 mEq/l. After warming to 36C, these were significantly reduced(P <0. 05) and became 144. 6mEq/1, 112. 4mEg/1 and 68. 13mEq/1 respectively. 2) There was a tendency to increasing of K+ cencentration in proportion to storage duration. 3) In the case of calcium, pre-warmed concentration of calcium was 4. 09 mEq/1 and there was no significant change after warming(P>0.05).