Serum fluorescein and p-aminobenzoic acid were measured during a urine pancreolauryl and an N-benzoyl-l-tyrosyl-p-aminobenzoic acid (NBT-PABA) test in 22 healthy controls, 17 patients with gastrointestinal nonpancreatic diseases (normal secretin-pancreozymin test), and 31 patients with abnormal exocrine pancreatic function due to chronic pancreatitis. The optimal cutoff point for separating normal from abnormal pancreatic function was after 210 min in the pancreolauryl test and after 150 min in the NBT-PABA test. The latter test was slightly less sensitive and specific than the pancreolauryl test. Serum tests seem to offer a practicable alternative to the established indirect pancreatic function tests in urine and may be used in the elderly and severely ill, as well as in outpatients in whom correct collection of the urine may be difficult.