A reliable method is described for the determination of conjugated and unconjugated bile acids in serum and jejunal fluid. Bile acids are extracted using reverse-phase octadecylsilane bonded silica cartridges and are separated into their unconjugated and conjugated fractions using the lipophilic anion exchanger diethylaminohydroxypropyl Sephadex LH-20 (DEAP-LH-20). The conjugated fraction can be separated into a glycine and a taurine fraction, using the same anion exchanger. The bile acids are measured using a hydroxysteroid dehydrogenase-fluorimetric assay for serum and a hydroxysteroid dehydrogenase-photometric assay for jejunal fluid. The normal fasting serum value of total 3 alpha-hydroxy bile acids amounts to 3.5 +/- 2.8 mumol/l (mean +/- SD, range 1.4-10.8, n = 22). The corresponding unconjugated bile acid fraction amounts to 39.9 +/- 11.2% (range 20.7-64.6%) of total bile acids. The concentration of conjugated bile acids became significantly elevated 30, and 60 min after a standard meal, whereas that of unconjugated bile acids remained unchanged. In jejunal fluid only conjugated bile acids are found, as well in fasting subjects as postprandial, 30 or 60 min after a standard meal.