It seems that in human gastroduodenal mucosal biopsy specimens from healthy persons there is a definite tendency toward a higher endogenous prostacyclin content in favour of women. This discrepancy is present in peptic ulcer disease, too. Smoking exerts an unfavourable effect on the gastric and duodenal mucosa. The target of this action is (among others) the endogenous prostacyclin content. In ventricular as well as duodenal ulceration there is a tendency toward decreased endogenous prostacyclin activity but (moderate) smoking, - as a continuous stimulus - seems to be capable of evoking higher endogenous prostacyclin levels. This phenomenon, most probably, constitutes a part of the reparative reactions against the noxa, i.e. smoking, itself. The results draw attention once again to a possible role of smoking in the development and healing of peptic ulcer disease.