We evaluated the efficacy of medical therapy, consisting of liquid bismuth subsalicylate prescribed either in combination with oral ampicillin (n = 15) or alone (n = 1), in the clearing of bacterial colonization on the antrum in 16 children with Campylobacter pylori-associated antral gastritis. We also examined the effects of medical treatment on altering the severity of associated antral inflammation. Eight patients had upper gastrointestinal tract hemorrhage, two had acute gastric outlet obstruction, and 10 had symptoms of episodic epigastric abdominal pain. Duodenal ulcers were demonstrated in 10 of the 16 patients; in the other six, C. pylori-associated antral gastritis was documented without evidence of acute peptic ulceration. Seven days after a 6-week course of medical therapy, repeat upper endoscopy plus mucosal biopsy specimens showed that C. pylori colonization of the antrum had cleared in 12 of the 16 (75%) patients. Inflammation in the antrum improved in all patients in whom colonization by C. pylori was eradicated. In contrast, in the four with persistent colonization of the antrum, the severity of antral gastritis had not improved (p less than 0.01). Clinical symptoms improved in 9 of 12 patients in whom C. pylori colonization was no longer present, whereas subjective symptoms were unaffected in those with continued bacterial colonization of the antrum (p less than 0.05). We conclude that oral bismuth subsalicylate, in conjunction with ampicillin, can eradicate C. pylori colonization of the antrum, and that clearing of C. pylori is correlated with an improvement in the associated antral gastritis and clinical symptoms. These findings provide additional support for the hypothesis that these gastric organisms could play an etiologic role in primary antral gastritis and peptic ulcer disease.