Helicobacter pylori infection is associated with exaggerated gastrin release. We investigated whether this abnormality was due to the bacteria or the immune response. Fasting and meal-stimulated 'total' and amidated gastrin were measured in 10 H. pylori-infected volunteers before eradication therapy, after 2 and 14 days of therapy, and 4 weeks after completion of therapy. The exaggerated meal-stimulated gastrin concentration remained unchanged after 2 days of therapy, although the polymorphonuclear cell infiltrate and H. pylori bacteria were no longer evident. The expected fall in gastrin concentration after 14 days of therapy was associated with a reduction in the density of mucosal mononuclear cells, suggesting exaggerated gastrin release was related to chronic inflammation or to H. pylori or its products. The effect of H. pylori on normal progastrin processing was also assessed; 2 control groups were included: 10 H. pylori-uninfected volunteers and 13 patients with H. pylori peptic ulcers. There was a significant difference in the proportion of circulating gastrins that were biologically active amidated gastrins between ulcer patients and uninfected controls (56.7 +/- 4% versus 33.8 +/- 4%, p < 0.001). The proportion of amidated to total gastrins did not increase after successful eradication.