Effect of hydrochlorothiazide on serum potassium level was studied in the hypokalemia-induced rats by the oral administration of glycyrrhiza extract (GE) for 4 weeks. According to the concentration of GE, serum potassium levels were found to be $5.8{pm}0.2,;5.4{pm}0.2;and;5.5{pm}0.2;mM/l$ after oral administration of 0.1, 0.2 and 0.5% GE solutions for 4 weeks, respectively, comparing $6.4{pm}0.2;mM/l$ in normal rats. The i.p. administration of hydrochlorothiazide (100mg/kg) showed no significant difference $(5.1{pm}0.3-5.2{pm}0.3;mM/l)$ in the decrease of serum potassium levels between these hypokalemia-induced rats and normal rats, regardless of the concentration of pretreated GE solutions. Therefore it was considered that the administration of hydrochlorothiazide did not worsen the hypokalemia induced by the long term administration of GE in rats.