We have studied gastric mucus secretion after carbenoxolone, zolimidine and prostanoic acid short term treatment (28 days) in patients with endoscopically demonstrated peptic gastric ulcer of the lesser curvature. Six patients were treated with carbenoxolone (300 mg/day), 6 with zolimidine (1200 mg/day) and 6 with prostanoic acid (2 g/day). All of them were submitted to gastric juice collection, before and after treatment, during 1 h at fast. On the samples of gastric juice, taken at 15 min intervals, the protein component (PC), glucosamine (GL), fucose (FU), the free N-acetyl-neuraminic acid (NANA) and sulphate groups (SG), were determined by biochemical methods. We have observed a significant increase of PC after zolimidine (P less than 0.02) and prostanoic acid (P less than 0.05) treatment, without significant variations of the other mucus components. No significant variations of mucus secretion after carbenoxolone treatment. If we compare the three drugs, we can see a significant increase of PC after zolimidine (P less than 0.005) and after prostanoic acid (P less than 0.001), compared with the results obtained after carbenoxolone. There are no significant variations of basal and stimulated (pentagastrin 6 mcg/Kg i.v.) secretory volume and acid output before and after treatment in the three groups of patients.