• Radiologic and biochemical abnormalities associated with nutritional hypophosphatemic rickets were discovered in a 945-g preterm infant despite daily supplementation with 800 to 1,600 IU of ergocalciferol (vitamin D2) and an elevated serum 25-hydroxyvitamin D concentration. Vitamin D supplementation was stopped, and the rickets was corrected by phosphorus supplement alone with the use of a unique technique of long-term, continuous nasogastric phosphorus infusion. Normophosphatemia was rapidly achieved and effectively maintained. Hypocalcemia did not occur at rates of infusion of 100 mg of elemental phosphorus per day. The data are consistent with specific phosphorus deficiency as the cause of rickets in this infant, rather than insufficient vitamin D intake or disturbed vitamin D metabolism. We speculated that continuous phosphorus infusion prevents the intermittent hyperphosphatemia of bolus phosphorus supplement and that continuous phosphorus infusion may be useful in the treatment of other hypophosphatemic states of infancy.