An in-vitro test of degradation of haptocorrin, a cobalamin-binding glycoprotein, was used to diagnose exocrine pancreatic dysfunction. This radioisotopic test (TDH) required only 50 microliters duodenal juice collected during endoscopy after stimulation with 1 U/kg secretin intravenously. The initial reaction mixture, composed of salivary haptocorrin saturated with cobalt-57-labelled cyanocobalamin and unsaturated intrinsic factor, was incubated with 25 microliters duodenal juice. The percentage of degraded haptocorrin was estimated from the proportion of labelled cyanocobalamin that was transferred from haptocorrin to intrinsic factor. The TDH result was 41.6 +/- 31.7% (SD) in a group of chronic pancreatitis patients (n = 22) and 91.5 +/- 4.8% in the control group (n = 47). The sensitivity and specificity for exocrine pancreatic dysfunction were estimated as 0.91 and 0.96, respectively, for a lower limit of normal values of 81.7%. A hyperbolic relation was found between the TDH and the trypsin or chymotrypsin activity in duodenal juice (p less than 0.001). In this study, the N-benzoyl-tyrosyl-p-aminobenzoic acid test was less sensitive than the TDH, since its result was abnormal in only 64% of the patients. The TDH was easier to carry out and less time-consuming than the determination of pancreatic enzyme output in duodenal juice collected after hormonal stimulation.