In 1982, a new spiral Gram-negative bacterium which was similar to those of the genus Campylobacter was isolated from the gastric mucosa of 11 patients with gastritis. From then on, the organism was isolated in a further 114 of 267 patients who underwent antral biopsy in Fremantle Hospital between January 1983 and September 1984. During 1984, the bacterium was cultured from 88% of patients in whom it was detected histologically, and was not cultured from any patient with histologically normal gastric mucosa. The new bacterium, pyloric campylobacter, grew in three days on brain-heart infusion blood-agar at 37 degrees C in an atmosphere with added CO2. All isolates tested were sensitive to penicillin, erythromycin, tetracycline, cephalosporins, gentamicin and bismuth citrate; 80% of isolates were sensitive to metronidazole or tinidazole. It is suggested that pyloric campylobacter infection is a major factor in the causation of dyspeptic disease and peptic ulceration. Antibacterial regimens directed against the bacterium may provide a permanent cure for these chronic disorders.