A small but significant rise in serum potassium level following succinylcholine administration has been observed in normal anesthetized patients. A dangerous increase in serum potassium concentrations after the administration of succinylcholine chloride has been reported in an increasing number of clinical conditions including burns, massive muscle trauma, tetanus and uremia. The hyperkalemia can be of sufficient degree to cause ventricular tachycardia and fibrillation. Serum electrolytes levels were measured in 40 healthy children during induction of anesthesia. They were less than 10 years old and were divided into 4 groups of 10 children each. Group l: Ketamine 2 mg/kg and succinylcholine 2 mg/kg Group llI: Thiopental 5 mg/kg and succinylcholine 2 mg/kg Group lll: Pretreatment with pancuronium 20 ug/kg followed in 3 min by ketamine 2 mg/kg and succinylcholine 2 mg/kg Group lV: Pretreatment with pancuronium 20 ug/kg followed in 3 min. by thiopental 5 mg/kg and succinylcholine 2 mg/kg. Venous blood samples for serum electrolyte estimation were obtained using a catheter placed in an antecubital vein. The following results were obtained: 1) Serum potassium concentration following administration of succinylcholine was significantly increased in group l (p<0.05), but not in group ll, lll, lV. 2) Peak changes of serum potassium concentration were much higher in group l than group ll and lll, and the peak change in group lV was decreased below control values. Variance analysis indicate a significant difference between group I and the others(pp<0.05). 3) The peak change in serum potassium concentration in group I was from 1 min. to 3 min. after succinylcholine. 4) Serum Na+, Cl- and CO2, content were not significantly changed after succinylcholine and statistically not significant in all the groups.