Abstract 1. 1. Capacity and affinity of duodenal 1,25(OH) 2D 3 receptors were measured in P depleted goats and in control animals kept on an adequate P supply. Plasma concentrations of P i Ca and vitamin D 3 metabolites and activity of plasma alkaline phosphatase were measured to characterize the effects of P depletion. 2. 2. During P depletion plasma P i concentrations decreased significantly whereas plasma Ca and alkaline phosphatase activity increased. No changes were recorded for plasma vitamin D 3 250HD 3 and 1,25(OH) 2D 3 concentrations. 3. 3. P depletion resulted in a significant decrease of the equilibrium dissociation constant K d of duodenal 1,25(OH) 2D 3 receptors without affecting the maximum binding capacity.