Eight patients in the state of ASA classification l, ll were investigate. Blood samples were collected before, just after, 30 minutes after and 60 minutes after induction of anesthesia. Glucose and electrolyte changes in relation to maintenance fluids in balanced and halothane anesthesia were as follows. 1) In both anesthetic techniques blood sugar level showed increasing tendency according to duration of anesthesia. 2) There were no specific changes in serum electrolytes related to type of anesthesia. 3) The administration of D/S and H/D showed a little increase in Na+ and Cl- level compared to the administration of just DsW. 4) The administration of H/d showed less increase in K+ level than the administration of DsW or D/S. 5) Just after induction of anesthesia the K+ level increased a little and decreased gradually thereafter.