This article reviews the evolution of functional testing of the pancreas in Japan for the diagnosis and treatment of chronic pancreatitis (CP), contrasting the pre- with the post-secretin test (S test) era. In the pre-S test era, the diagnosis was based on symptoms, clinical findings, fasting serum diastase levels, and the vagostigmin- and ether-stimulation test unless morphologic evidence was available. The S test and CCK-pancreozymin (PZ) test (PS test) were introduced into Japan around 1963 and have been used as the gold standard of the exocrine pancreatic-function test. Through a series of attempts at standardization in 1971, 1985, and 1987, the method was standardized to collect duodenal juice for 60 min through a double- or triple-lumen tube after a bolus or during a continu-ous i.v. injection of secretin (100 U). The S test, however, is an invasive and cumbersome procedure. As a result, N-benzoyl-L-tyrosal-paminobenzoic acid (BT-PABA) testing and fecal chymotrypsin testing were introduced into Japan in the middle and late 1970s, respectively. Although simple and noninvasive, these two methods were found have lower sensitivity and specificity than the conventional S test. These two methods, therefore, are presently used more often for monitoring the course of disease and therapeutic effects. Additionally, the glucose tolerance test can be performed to detect endocrine pancreatic insufficiency.