BACKGROUND: The purpose of this study is to evaluate the effects of crystalloid solutions on the arterial blood gas and electrolytes in spinal (n = 58) and hip joint surgery (n = 2). METHODS: Sixty patients were randomly divided into three groups according to the kind of crystalloid solutions. Group 1 patients (n = 20) received Hartmann's solution (HS), group 2 patients (n = 20) received HS plus normal saline (NS) in a 1 : 1 volume ratio, and group 3 patients (n = 20) received NS. Arterial blood gas and electrolytes were measured after induction and at the end of the operation. RESULTS: The replacement volumes of the crystalloid solutions in groups 1, 2 and 3 were 2545 +/- 931, 3050 +/- 1013 and 3240 +/- 1056 ml, respectively. The degree of the change in pH from after induction until the end of the operation was the greatest in group 3 (0.125) than in group 1 (0.04) and group 2 (0.079) (p < 0.05). The degree of the changes in the serum chloride value in groups 2 (9.1 mEq/L) and 3 (12.1 mEq/L) was greater than that in group 1 (4.2 mEq/L), respectively (p < 0.05). In the relationships among the parameters in group 3, the pH values tended to decrease with increasing volume replacements of NS (P = 0.005); and the chloride values tended to increase with increasing volume replacements of NS (P = 0.005). CONCLUSIONS: The results suggest that HS is the superior crystalloid solution because there were less changes in acid-base balance and chloride value than when NS was infused alone. HS did not alleviate the changes of acid-base balance and chloride value caused by NS when both of them were infused at the same time.