Metabolites of 1.alpha.,25-dihydroxy[3.alpha.-3H]vitamin D3 in rat bile were studied. The water-soluble metabolites (77-91% of the total bile radioactivity) are predominantly acids (retained by DEAE-Sephadex chromatography) that become chloroform soluble after methylation with diazomethane. Calcitroic acid was isolated from this fraction (after conversion to the methyl ester) and unambiguously identified by chromatographic and mass spectrometric studies. The chloroform phase of extracted bile contains small amounts (1.1-8.1% of the metabolites in bile, dependent on dose given) of unchanged 1.alpha.,25-dihydroxyvitamin D3 and no 1.alpha.,24(R),25-trihydroxyvitamin D3. The chloroform phase contained a mixture of 24-dehydro- and 25-dehydro-1.alpha.-hydroxyvitamin D3 and calcitroic acid methyl ester. The latter compound was an artifact resulting from the use of methanol as part of the solvent mixture for the initial bile extractions.