We have examined endoscopic clinic patients in three widely different geographic regions of Peru (the coast, the Sierra of the Andes Mountains, and the Amazon jungle) for the presence of Helicobacter pylori infection associated with active gastritis. The overall rates of infection were high (80% or greater) in all three zones and rates for men were approximately 10% higher than for women in the same zone. Men and women in the Sierra and jungle areas had significantly higher rates of infection than did those on the coast. There was no significant difference between the three populations with respect to the relationship between infection and grade of gastritis.