A combination secretin-Lundh test was performed on 14 healthy established smokers to determine if smoking inhibited pancreatic secretion and therefore might contribute to the production of a duodenal ulcer. Seven of the patients studied smoked more than 20 cigarettes per day and were classified "heavy smokers". The remaining seven patients smoked less than 20 cigarettes per day and were classified "light to moderate smokers". The volume and bicarbonate output of the pancreas were lowered in both groups of patients after smoking one cigarette. This apparent side effect of nicotine may possibly play an important role in the production of duodenal ulcers in smokers by producing an acid milieu in the duodenum. Tryptic activity was unaffected by smoking.