A murine model for testing cytokine production stimulated by Helicobacter pylori is described. H. pylori induced significantly lower levels of TNF-alpha and IL-1 alpha compared to Escherichia coli or Pseudomonas aeruginosa when injected intravenously. The mean TNF-alpha concentration in serum during 6 h after stimulation with H. pylori was 0.2 ng/ml, whereas E. coli induced 4.7 ng/ml and P. aeruginosa 6.0 ng/ml. This was not explained by rapid elimination of H. pylori as bacteria were present for at least 3 h in the blood. The difference in cytokine induction may be a reflection of the bacteria's different biological qualities. E. coli and P. aeruginosa are both capable of causing systemic disease, whereas H. pylori causes only a local, often low grade, inflammation in the gastric mucosa.