Strains of Helicobacter pylori which express the product of the cytotoxin associated gene A(CagA) are associated with duodenal ulceration. Also there is evidence that the presence of serum IgG antibodies to CagA is associated with an increased risk of gastric cancer of the intestinal type. Gastric atrophy is a precursor of intestinal-type gastric cancer so we have investigated whether antibodies to CagA are associated with gastric atrophy. In H. pylori infected patients, IgG antibodies to CagA were present in 24/38 (63%) of non-ulcer patients with atrophy compared with 13/40 (33%) of patient-controls with neither atrophy nor ulcer (P < 0.02). CagA antibodies were also more prevalent in patients with duodenal ulcers; 15/20 (75%) or gastric ulcers 5/5 (100%) than in the patient-controls (P < 0.005 and < 0.02 respectively). These results show that circulating IgG antibodies to CagA are associated with gastric atrophy, as well as peptic ulcer disease. Atrophy is a precursor of gastric cancer so support the hypothesis that certain strains of H. pylori are more likely to cause gastric cancer.