The effect of Ca/P ratios and pH on absorption of Ca and P was measured in vivo in dogs with healed intestinal loops. With Ca constant, variations either of P/Ca or pH did not alter Ca absorption. With no phosphorus, Ca absorption was significantly depressed. Phosphorus absorption was proportional to phosphorus concentration in this perfusate, and was depressed by a lowered pH. With a high Ca concentration, percentage Ca absorbed rose, and was unaffected by P/Ca ratio or pH. It was concluded that P/Ca ratios and pH are not important as factors which limit calcium or phosphorus absorption, in vivo, within reasonable physiologic dietary concentrations of these elements.