Fasting and postprandial concentrations in serum of 3αhydroxy-bile acids and gamma-glutamyl transferase were measured in 138 consecutive patients, 62 with (D) and 76 without (D) hepatobiliary disease. The maximum efficiencies of the three tests - that is, the fractions of patients allocated correctly to the D or D group at the optimum discrimination values - were 0.85, 0.84, and 0.83, respectively. Furthermore, the predictive values and nosographic sensitivities and specificities were rather similar. When the three tests were combined, the nosographic sensitivity increased significantly to a value of 0.84, and the corresponding specificity was 0.91. The diagnostic value of the absolute postprandial increase in serum bile acid concentration was slightly inferior to the diagnostic values of the fasting and postprandial serum bile acid concentrations and, finally, the relative postprandial serum bile acid increase was of no diagnostic value at all.