Basal and pentagastrin- or insulin- stimulated secretion was studied in 72 non ulcer dyspectic patients (NUD), in 289 non operated duodenal ulcer patients (DU), and in 30 DU, before and after highly selective vagotomy (HSV). Acidity, proteolytic activity, choline indicating the presence of duodenogastric refluxed material and sialic acid bound to mucus glycoprotein, marker of mucus erosion, were measured. Basal and pentagastrin-stimulated acid and pepsin secretions in NUD were significantly reduced with regard to those in DU. Sialic acid content was weak in basal secretion and markedly increased in response to pentagastrin reaching the values observed in DU. DU basal secretions of acid and of pepsin were modulated according to the stimulating secretory mechanism. Mucus glycoprotein erosion was related to pepsin mucolytic activity and/or to the presence in gastric juice of refluxed material. In DU the increase of peptic mucolysis corresponded to a biological signal of the ulcer attack when no duodenogastric reflux was identified. High values pepsin output in basal secretion and in response to insulin and of basal sialic acid content combined with a pepsin/acid basal output ratio higher than 80 were biological arguments anticipating the efficacy of HSV in DU. Multiparametric analysis of gastric secretion allows to evaluate the ratio between aggressive factors and mucosal defense corresponding to an equilibrium in NUD and to greater aggressivity in DU whose intensity is related to the course of disease.