Corrinoids were extracted with hot ethanol from human plasma and faeces and separated by high-performance liquid chromatography. The corrinoids (cobalamin and cobalamin analogues) were quantified in the eluted fractions by a dual radioisotope assay using as binders intrinsic factor and haptocorrin to detect cobalamin and total corrinoids, respectively. Recoveries ranged from 37.7 +/- 5.1% for hydroxycobalamin to 75.0 +/- 9.1% for cyanocobalamin. In plasma, the main forms of cobalamin were the coenzymes methylcobalamin and 5'-deoxyadenosylcobalamin (32.1 +/- 13.4 and 28.4 +/- 12.3%, respectively, of total corrinoids). The cobalamin analogue fraction of plasma was eluted with a retention time close to that of cobinamide and of deoxyadenosylcobalamin. In the faeces, most of the corrinoids separated were detected better by the haptocorrin assay than by the intrinsic factor assay. One corrinoid peak was eluted with the same retention time as cobinamide. This peak was detected by haptocorrin assay but not by intrinsic factor assay. It could therefore correspond to cobinamide.