Paf-acether synthesis by Helicobacter pylori. Clinical studies suggest that Helicobacter pylori may play a role in the pathogenesis of gastroduodenal ulcers in man but direct evidence of mucosal injury by this microorganism is still lacking. Paf-acether (paf) causes a number of disorders including ischaemic bowel necrosis and gastroduodenal ulceration. Since paf is produced by Escherichia coli, we investigated whether it could be synthesised by H pylori. Five H pylori isolates were collected from antral biopsy specimens from patients with gastritis and duodenal ulcer and cultured with selective antibiotics. Colonies obtained from both blood agar and brucella broth medium were used. Paf was determined by platelet aggregation assay after ethanolic extraction and subsequent purification by high performance liquid chromatography. Paf was detected in H pylori in blood agar plates (680 (390) pg paf/1 x 10(6) organisms) but not in bacteria cultured on brucella broth medium. Supplementation of the latter medium with lyso paf and acetyl-CoA, two paf precursors present in high amounts in the mammalian intestine, induced paf production in three of five isolates. The platelet aggregating material extracted from H pylori exhibited biological and physiochemical characteristics identical to those of paf released from eukaryotic cells. These findings suggest that H pylori may add to the local production of paf in inflamed gastric mucosa. 