Since gastric symptoms are frequent in uremic patients, we have studied the prevalence and significance of Campylobacter pylori infection in patients with chronic renal failure. The prevalence of serum IgG antibodies to C. pylori in 50 patients on regular dialysis treatment (44%) was similar to that of a control group of 40 blood donors (45%), but was significantly lower (p = 0.0001) than that in 31 patients with peptic ulcer disease (93%). Furthermore, 11 of the 50 patients with chronic renal failure and a history of documented peptic ulcer disease had a similar prevalence of antibodies to C. pylori (45%) as did the 39 chronic renal failure patients without previous peptic ulcer (44%), which was significantly lower (p less than 0.01) than that in the control group of peptic ulcer patients (93%). Of 10 patients with chronic renal failure (6 with and 4 without gastric complaints) studied by endoscopical biopsies, two had chronic active antral gastritis and were positive for C. pylori by histology, culture and had IgG antibodies in their sera, while one patient with normal antral mucosa had IgG antibodies but was negative by culture and histology. Thus, this study shows that there is no predisposition to C. pylori infection among patients with chronic renal failure, and that C. pylori infection does not play a significant role in the ulcer diathesis in these patients.