The maximum bindings of ouabain to erythrocytes (Bmax), serum sodium (Na) and potassium (K) concentrations, and urinary excretions of Na and K were measured in 72 normal children, on a normal diet, aged 10 to 15 years. Bmax did not show any significant correlation with serum Na and K, and urinary Na and K excretions. These findings suggest that Bmax, which has been reported to be low in primary hypertension, may not be influenced by Na and K balances.