In 16 children with malabsorption syndrome, out of which 5 had impaired lipid absorption or diarrhoea, and in 14 children in the control group the concentrations of vitamin D and 25 OH D3 were determined after oral administration of vitamin D in dose of 1200 U/kg.b.wt. or 12000 U/kg.b.wt. No decrease in initial 25 OH D3 concentrations was noted in children with malabsorption syndrome (40,5 +/- 0,7 ng/ml) in comparison with the control group (40,0 +/- 0,4 ng/ml). In children with impaired lipid absorption and diarrhoea the 25 OH D3 concentration was 33,6 +/- 2,4 ng/ml. After oral administration of vitamin D in small doses no differences were noted in the increase in vitamin D and 25 OH D3 concentrations in children with malabsorption syndrome or the control group. After administration of vitamin D in the dose 10 times higher no difference in the increase in vitamin D concentration was noted in children with malabsorption syndrome and the control group. However the increase in 25 OH D3 concentration in children with malabsorption syndrome was 49,8 +/- 1,2 ng/ml and 145,0 +/- 3,5 ng/ml in the control group. In the children with impaired lipid absorption and diarrhoea decreased vitamin D and 25 OH D3 concentrations were noted. This means that physiological doses of vitamin D in children with malabsorption syndrome are sufficient to supply vitamin D. Diarrhoea and impaired lipid absorption however, are indications for stimulation of skin synthesis of vitamin D.