We have developed a 14C-urea breath test to follow the course of Helicobacter felis infection in mice. Peak 14CO2 production occurred approximately 8 min after substrate administration. The test values were compared to those from a rapid urease test and correlated with the presence of pathogens by histology. The sensitivity was 99%, specificity 91%, positive predictive value 95% and negative predictive value 99% when the assay was conducted in fasted mice. We conclude that in mice the breath test analysis is a useful noninvasive method for detecting the presence of H. felis or for evaluating therapeutic agents affecting growth or survival of the organism.