To test whether Helicobacter pylori may contribute to the inflammatory response following myocardial infarction, the levels of IgG antibodies to Helicobacter pylori and some parameters of leukocyte activity were measured in 63 patients and 61 comparable controls. Helicobacter pylori-positive patients showed a significantly higher expression of the adhesion molecule LFA-1 on neutrophils than Helicobacter pylori-negative patients (433+/-29.0 vs. 398.8+/-38.9 mean fluorescence channels; P<0.0001), whereas no significant difference for any parameters tested was found in control subjects. These data suggest a role of Helicobacter pylori in inducing a leukocyte response following myocardial infarction.