In 23 very low birth weight infants the influence of mineral supplementation with 0.4 mmol calciumgluconate and 0.2 mmol glucose-1-phosphate/dl human milk on concentrations of 25-OH-D3, parathyroid hormone, calcitonine, calcium, phosphorus and activity of alkaline phosphatase was studied on days 3, 8, 28 and 56. On days 28 and 56 respectively, degree of bone mineralisation was classified. 8 preterm infants received supplementation before day 28, 7 infants after day 28, 8 infants had no supplementation. All preterm infants received beginning with day 7 vitamin D3 1000 IU/day. In all preterms mean concentrations of 25-OH-D3 were normal and increasing with age. Concentrations of parathyroid hormone and calcitonine were first of all increased and decreased with age, especially in supplemented infants. Light metabolic bone disease without fractures occurred in 4 infants of supplemented groups. Non-supplemented group contains 5 infants with severe metabolic bone disease without fractures. Results indicate intact metabolism and secretion of 25-OH-D3, parathyroid hormone and calcitonine. Decrease of calcitonine concentration in mineral supplemented preterms is a reference to a better mineral supply. Mineral supplementation is followed by an increase in bone mineralisation with prevention of severe metabolic bone disease.