Prolonged stimulation with pentagastrin in doses of 100 and 500 ng h-1 kg-1 was performed in nine healthy subjects. A plateau in gastric secretion was reached after 90 min with 100 ng h-1 kg-1 and 500 ng h-1 kg-1 resulted in a secretory plateau after 60 min. When the plateau was reached the acid secretion rate was constant for the rest of the study, that is 4 h after beginning the pentagastrin infusion. Medians and interquartile ranges of acid output were 4.9 (3.7-5.2) and 8.1 (5.8-9.5) mmol of H+/30 min. We conclude that no 'fade' of gastric acid secretion occurs during 4 h of submaximal pentagastrin stimulation in normal subjects, and that the time required for reaching a secretory plateau is dependent on the dose of pentagastrin.