We studied 26 Nigerian children with active rickets (13 boys, 13 girls), aged 1 to 5 years, and compared results of biochemical studies with those of healthy control subjects. The plasma 1,25-dihydroxyvitamin D level was elevated (568 +/- 317 pmol/L) and the 25-hydroxyvitamin D level was (36 +/- 28 mol/L) in the children with rickets compared with the control subjects (369 +/- 134 nmol/L and 69 +/- 22 nmol/L, respectively). The results suggest that rickets in Nigeria is largely the result of calcium deficiency and that vitamin D deficiency and possibly end organ resistance may be contributory factors.