We studied 211 unselected, healthy, adult patients scheduled to undergo elective ambulatory surgery to determine whether the volume or pH of gastric fluid at induction of anesthesia is correlated with the duration of the preoperative fluid fast. Patients were instructed that they must not eat any solid food after midnight but that they were permitted to drink 150 ml of tea, coffee, apple juice or water until 3 hours before their scheduled time of surgery. Patients with gastric disorders and those taking medications that affect gastric motility or secretion were excluded. No premedicant drugs were given. Following induction of general anesthesia the gastric fluid was aspirated through an orogastric tube, its volume recorded and its pH measured with a calibrated pH meter. The patients were retrospectively assigned to one of four groups according to the interval from last fluid ingestion until induction of anesthesia (less than 3 hours, 3 to 4.9 hours, 5 to 8 hours and nothing after midnight). The mean values and extremes for gastric fluid volume and pH were similar in the four groups. We conclude that healthy patients should be allowed to ingest fluid until 3 hours before elective ambulatory surgery.