SUMMARYThe relationship between smoking and gastric secretory capacity was studied in 201 25-40 year old healthy subjects with normal laboratory data and no gastrointestinal lesions. Basal acid output (BAO) and peak acid output (PAO) were determined in all, and basal and stimulated pepsin outputs were measured in 85 participants. The accuracy of the patients' statements was checked by urinary nicotine assay. Basal acid output and PAO were significantly higher in male smokers (n=55) than in male non-smokers (n=49). In women PAO in smokers (n=38) was higher than in non-smokers (n=59). Female smokers (n=38) had a higher pepsin output than female non-smokers (n=23). Eight variables were considered in relation to BAO and PAO: age, height, weight, alcohol abuse, smoking habits, duration of smoking habit, number of cigarettes per day, and the product of years of smoking multiplied by daily number of cigarettes. The daily number of cigarettes x years of smoking was most closely correlated with BAO and PAO by stepwise multiple linear regression analysis. It was concluded that smoking is related to increased gastric acid capacity.The influence of acute nicotine abuse on gastric acid secretion has been investigated by many authors. The results of these studies are highly controversial; whereas some have reported an increase in gastric secretion under basal conditions1-3 or under H2-receptor antagonists,4 or a decrease after stimulation by pentagastrin,5 others have found no significant changes.6-0 In a previous study, we found that duodenal ulcer patients who smoked had a higher peak acid output than did non-smokers.11The present study is designed to find out whether there is a relationship between smoking habits and gastric acid secretion in healthy subjects without peptic ulcer disease. Methods PATIENTSAll patients arbitrarily assigned to one of us (SM) by the reception of our outpatient department for general clinical investigation were asked to volunteer for gastric analysis, provided they met the