A pancreatic function test (PFT) by peroral intake of a synthetic peptide (N-benzoyl-L-tyrosyl-P-aminobenzoic acid) was performed on 29 healthy controls and 131 patients with various pancreatic diseases in order to evaluate its validity and limitations. PFT was found to be a simple and useful exocrine pancreatic function test with good reproducibility. PFT values were significantly lower in patients with noncalcified chronic pancreatitis, pancreatolithiasis, pancreatic cancer, pancreatectomy or acute pancreatitis than in healthy controls. Furthermore PFT values were abnormal in 13.6 percent of 22 patients with suspected chronic pancreatitis, 78.1 percent of 32 patients with noncalcified chronic pancreatitis, 81.5 percent of 27 patients with pancreatolithiasis and 88 percent of patients with pancreatic cancer. Mild damage of the pancreas could not be detected by PFT, though moderate to severe damage could be in most cases. As for pancreatic cancer, the PFT values were not abnormal unless the main pancreatic duct was obstructed within 6 cm of the Vaterian papilla, and as for chronic pancreatitis, values were abnormal only when dilatation of the pancreatic duct was accompanied by stenosis, irregular margin, rigidity and/or obstruction. Evaluation of patients who had undergone a pancreatectomy indicated that PFT values were abnormal when more than the proximal half or the distal three-fourths of the pancreas was resected. PFT was useful in following up recovery from acute pancreatitis. PFT is slightly less sensitive than the pancreozymin secretin test in detecting exocrine pancreatic dysfunction, and a normal PFT value does not necessarily rule out pancreatic disease.