Among genetically hypertension-prone rats, dietary sodium (chloride) was demonstrably hypertensinogenic and potassium (chloride) antihypertensinogenic. On diets containing the same NaCl but different KCl concentrations, mean blood pressure was greater in rats receiving less dietary potassium, i.e., diets with a higher Na/K molar ratio. On diets with different absolute concentrations of NaCl and KCl, but the same Na/K molar ratios, rats on the higher absolute NaCl intakes had the higher blood pressures. On diets with different absolute concentrations of NaCl and KCl, and different Na/K molar ratios, a group on a lower absolute NaCl intake but with a higher Na/K ratio could have more hypertension than a group on a higher absolute NaCl intake but with a lower Na/K ratio. At equivalent molar ratios, the respective effects of these two ions on blood pressure were dominated by that of sodium. It was concluded that the dietary Na/K molar ratio can be an important determinant for the severity, or even development, of salt-induced hypertension. The mechanism of the moderating effect of potassium on sodium-induced hypertension was unclear.