The mean ± SEM of the cord, 48-hr, and 7-day values for scrum calcium, magnesium, human calcitonin (HCT), parathyroid hormone (PTH), and 25-hydroxy-vitamin D (25-OHD) for premature and term infants can be seen in Table 1. Mean cord calcium concentrations were similar for term and premature infants. Serum calcium concentrations fell in both term and premature infants at 48 hr, but decreased more in the premature infants (from 10.23 ± 0.30 to 8.74 ± 0.19 mg/dl) than in the term infants (from 10.5 ± 0.26 to 9.6 ± 0.23 mg/dl). Serum calcium values increased from 48 hr to 7 days in both groups, and there was no significant difference between term and premature infants' serum calcium concentrations (10.6 ± 0.28 and 10.12 ± 0.3 mg/dl, respectively) at that time. There was no significant difference between term and premature cord scrum magnesium concentrations. Serum magnesium concentrations increased similarly by 48 hr in both groups and remained at these concentrations at 7 days of life. Serum HCT concentrations were elevated above normal adult levels (71.9 ± 6.6 pg/ml,