The effect of high dietary pyridoxine and magnesium on tissue electrolytes was studied in day-old broiler-type male chicks. There were 15 treatments of 875, 1375 and 1875 mg. magnesium/kg. diet and pyridoxine at 1, 4, 31, 301, 3001 mg./kg. diet in a 3 x 5 factorial block design. The sodium concentration of the liver decreased linearly with increasing dietary magnesium concentration expressed as log 10. In the kidney, no such effect was observed. The response of sodium concentration in these two tissues to increasing dietary pyridoxine, also expressed as log 10, was curvilinear, decreasing to minimum concentrations at pyridoxine intakes estimated to be equal to 40 mg./kg. of diet for the liver and 50 for the kidney and thereafter increasing. Potassium concentration of the liver exhibited opposite trends to those for sodium concentration but the responses to dietary magnesium were not consistent at each dietary pyridoxine concentration. Kidney potassium content followed essentially opposite trends to those of sodium. Kidney calcium decreased with increases in either dietary magnesium or pyridoxine, but the decreases were not consistent. The magnesium content of the kidney tended to increase with increases in dietary magnesium. Dietary pyridoxine resulted in a curvilinear response only in those chicks fed the 1875 mg. diet, decreasing to a minimum value at a pyridoxine intake of 26 mg., and increasing at higher pyridoxine dietary concentrations. No significant effects on sodium, potassium, calcium and magnesium concentrations in the heart were observed. It was speculated that the maximum potassium retention estimated to occur in the livers of birds consuming a diet containing 48 mg. pyridoxine/kg. diet might be due to increased glycogen turnover or increased phosphorylase activity.