Acute Helicobacter pylori associated gastritis causes achlorhydria, a powerful stimulus to gastrin secretion. If H pylori infection is acquired primarily in early childhood, then the degree of hypergastrinaemia in seropositive children should be age dependent. Anti-Helicobacter antibodies and fasting gastrin concentrations were measured in 439 children aged 4 to 13 years attending hospital for routine day case surgery not connected with any gastrointestinal disorder. Thirty per cent were seropositive for H pylori. There was an inverse relationship between the fasting gastrin concentration and age; the mean fasting gastrin in children aged 4-5 years, 155 ng/l, was significantly higher than that seen in children aged 12-13 years, 90 ng/l. The more noticeable hypergastrinaemia seen in young children with H pylori associated gastritis may reflect achlorhydria associated with acute H pylori infection and suggests that this is primarily acquired in early childhood.