1. We have used pigs with inherited vitamin D-dependent rickets type 1 to study the effect of 1,25-dihydroxyvitamin D deficiency on the metabolic clearance rate of 3H-1,25-dihydroxyvitamin D3 infused to steady-state levels in plasma.
2. Plasma levels of 1,25-dihydroxyvitamin D were 24 ± 1 (sem) pmol/l in the hypocalcaemic, homozygous piglets and 196 ± 27 pmol/l in their normocalcaemic, heterozygous siblings.
3. The metabolic clearance rate of 1,25-dihydroxyvitamin D3 was the same in both normal heterozygous (0.90 ± 0.02) and hypocalcaemic, homozygous piglets (0.90±0.01 ml−1 min−1 kg−1 metabolic bodysize).
4. We conclude that a deficiency of circulating 1,25-dihydroxyvitamin D does not influence the clearance of 1,25-dihydroxyvitamin D3 from the circulation of pigs.