Circulating concentrations of 1,25-dihydroxyvitamin D, 24,25-dihydroxyvitamin D and 25-hydroxyvitamin D were measured in 21 anephric subjects. 13 subjects had no therapy with vitamin D, dihydrotachysterol or lα-hydroxyvitamin D<sub>3</sub>. In 7 subjects of this group 1,25-dihydroxyvitamin D was undetectable ( < 5 pmol/l). In the other 6 patients concentrations ranged from 10 to 43 pmol/l (reference value 111 ± 33 pmol/l). All subjects taking high doses of vitamin D showed detectable 1,25-dihydroxyvitamin D concentrations in the same range. Dihydrotachysterol therapy caused spuriously high ‘1,25-dihydroxyvitamin D’ values, probably by interference of a metabolite of dihydrotachysterol in our assay. In subjects on vitamin D or dihydrotachysterol therapy 25-hydroxyvitamin D concentrations were significantly elevated (314 ± 146 nmol/l and 98 ± 19 nmol/l, respectively; reference value 52 ± 22 nmol/l). Concentrations of 24,25-dihydroxyvitamin D were only measured in subjects without vitamin D<sub>2</sub> intake. In general very low but detectable concentrations were found. One subject on a high dose of vitamin D<sub>3</sub> showed a 24,25-dihydroxyvitamin D<sub>3</sub> concentration of 10.2 nmol/l (reference value 4.4 ± 2.9 nmol/l). Our results therefore confirm earlier reports on extrarenal synthesis of 24,25-dihydroxyvitamin D and suggest that there may be extrarenal production of 1,25-dihydroxyvitamin D as well.