Using commercially available radioimmunoassays, bile acids were measured in the serum of 378 healthy probands. The following values were found: conjugated cholic acid 0.36 +/- 0.38 mumol/l (95% percentile 1.28 mumol/l) (CG-radioimmunoassay from Abbot); sum of the various conjugated cholanic acids 2.8 +/- 1.58 mumol/l (95% percentile 5.98 mumol/l) (CBA-radioimmunoassay from Becton-Dickinson); sulphate glycolithocholic acid 0.57 +/- 0.33 mumol/l (95% percentile 1.23 mumol)l) (SLCG-radioimmunoassay from Abbot). The values showed a normal logarithmic distribution. No sex-specific differences were found between similar age groups of the 207 male and the 171 female probands. In 50 probands, serum concentrations were followed over a period of 3 hours after a standardized meal. Conjugated cholic acid showed a 5-fold postprandial increase, compared with the concentrations measured in fasting probands. In 48% this maximum was reached within 60 minutes, in 32% within 2 hours, and in 20% within 3 hours. The concentrations of sulphate glycolithocholic acid were subject to only slight postprandial variations, which did not appear until the second or third hour.