The saline load test is a popular method to demonstrate gastric retention. This technique, however, does not permit evaluation of volumes contributed by gastric secretion. We have studied 11 normal subjects and 7 patients with pyloric outlet obstruction using a dyedilution technique. We measured simultaneously rates of water secretion, fractional emptying rates, total intragastric volumes, and the fractions of gastric volume contributed by gastric secretion both during fasting and following a 250-ml water load. Total intragastric volume was significantly increased in patients with outlet obstruction compared to normal subjects both during fasting and following the water load (P less than 0.01). This increase resulted from significantly increased water secretion (P less than 0.01) combined with significantly decreased gastric emptying (P less than 0.01). Thus, gastric retention produced in patients with outlet obstruction by delayed emptying appears to be magnified by gastric hypersecretion of water. These data in no way invalidate the use of the saline load test in the diagnosis of gastric retention states, but help define the role of gastric secretion in the residual volumes measured following the load.