We examined the relationship between bone mineralization, measured by single photon absorptiometry, and blood phosphate and alkaline phosphatase concentration in 71 preterm neonates. Although both alkaline phosphatase and phosphate concentrations were significantly related to bone mineral content, and alkaline phosphatase concentrations were related to bone mineral content relative to weight, each could only explain a small amount of the variation in bone mineralization. Hence, concentrations of neither could be used to identify those neonates with the greatest bone mineral deficits.