In this study, the diuretic activity of powdered cherry stalk was evaluated in 13 healthy volunteers by means of their water balance. In addition to biochemical parameters, such as urinary electrolyte concentration, osmolality and any adverse reaction were determined. The capsules of cherry stalks were administered at an equivalent dose of 2.0 grams of the plant per person. Urinary biochemical determination was made of concentration of electrolytes (sodium, potassium, chloride and calcium), urinary volume and osmolality by standard laboratory procedures. Statistical evaluation was performed by Student's-t and Wilcoxon rank tests. After administration of cherry stalk, the mean of urine calcium, sodium, chloride, and urine volume increased, but the amount of urine potassium and urine osmolality did not change. No adverse reaction was observed. Powdered C. avium stalk increased mild urine volume confirming thus the claimed diuretic effect of the herb. Administration of cherry stalk caused urinary sodium and chloride rising less than loop diuretics but higher than the others. Because of rising calcium excretion, it should be used with cautious in those with urolithiasis.