We conducted a prospective, double-blind study of 43 preterm infants to examine the effect of a single calcium gluconate infusion as therapy for neonatal hypocalcemia on serum calcium concentrations and hypocalcemic signs in preterm infants with low total serum calcium concentrations. Total and ionized serum calcium was measured and signs of irritability, jitteriness, and twitching were scored (scale 0-9) by blinded observers before and after receiving one dose of either calcium gluconate (100 mg/kg) or placebo (normal saline). Total and ionized serum calcium increased 3 to 6 hours following the calcium, but not the placebo, infusion. Of the infants with hypocalcemic signs, the average score of hypocalcemic signs decreased in the 11 calcium-treated infants; the 12 infants with hypocalcemic signs showed no change of hypocalcemic signs following treatment with placebo. We conclude from this study that a single dose of calcium gluconate (100 mg/kg) in hypocalcemic preterm infants raise total and ionized serum calcium and decrease clinical signs of hypocalcemia.