There has long been disagreement about various aspects of the structure and function of the "gatekeeper" (Greek pyloros, from pyle = gate and ouros = guard). In recent years the problem has often been mentioned in anatomy, physiology, gastroenterology, radiology and even in nuclear medicine. For instance, while referring to manometric and gastric emptying studies, Schu- urkes and van Nuenten (1984 ) pointed out that there was considerable contro- versy as to whether a true pyloric sphincter existed in most species, and espe- cially in man. According to Reeve (1981) many functional aspects of sphincters are poorly understood; the exact mechanism of control of the transfer of chyme from stomach to duodenum through the pylorus is still not clear. Malagelada (1983) states that controversy surrounds the motor activity and function of the antro- duodenal junction; there is disagreement as to whether the pylorus functions as or as an integral part of the distal antrum. Ehrlein et al. (1984) a separate unit reiterate that pyloric motility is poorly understood, and according to Funch- Jensen (1987) there are many unsolved questions. Malagelada (1990) states that the stomach performs multiple functions with a deceivingly simple anat- omy; this is regarded as the key to the investigator's frustration when trying to uncover its secrets. One source of the many controversies surrounding the pylorus may be species differences, according to Schulze-Delrieu et al. (1984).