This patient was disease free immediately after surgery. At this 6-month assessment, fasting hypergastrinemia was present 1 day after discontinuing ranitidine therapy, 600 mg every 6 hours, suggesting that the disease had recurred; however, achlorhydria was also present at this time. Two days after discontinuing ranitidine therapy, basal acid output (BAO) increased and the fasting serum gastrin level decreased to within the normal range, showing that the patient was still disease free and had instead developed physiologic hypergastrinemia secondary to ranitidine-induced achlorhydria. The dotted line represents the upper limit of normal for the fasting serum gastrin level. See Methods section for definition of recurrence.