The oral pancreatic function test with N-benzoyl-L-tyrosyl-p-aminobenzoic acid was performed on 24 healthy test subjects, and its toxicity was examined. Eight patients with restricted renal function and known renal disease were also investigated. The pancreatic function test and the same procedure using free p-amino-benzoic acid were performed at 2-3-day intervals. During all the investigations with the pancreatic function test, no clinical side effects were observed. All parameters investigated at all the test times fell within the normal range. No toxicity of N-benzoyl-L-tyrosyl-p-amino-benzoic acid could be found. The excretion of p-aminobenzoic acid after administration of N-benzoyl-L-tyrosyl-p-aminobenzoic acid ws greatly reduced in all patients with restricted renal function. Four of eight patients also showed essentially no increase in excretion rate when free p-aminobenzoic acid was given instead of the peptide. It is therefore not possible to correct the pancreatic function test results in patients with renal insufficiency by calculating the ratio of p-aminobenzoic acid excretion after peptide intake to that after free p-aminobenzoic acid ingestion. Adequate renal function is therefore a prerequisite for the pancreatic function test.