The aetiology of infantile hypertrophic pyloric stenosis (IHPS) remains unclear. The aim of this study was to test the hypothesis that a common bacterium, Helicobacter pylori (HP) may be implicated in the pathogenesis of IHPS. Thirty-nine consecutive infants with confirmed IHPS had their stool analysed with an enzyme immunoassay for the presence of HP. An age/sex-matched group of infants with unrelated surgical conditions were also tested. No positive results for the presence of HP stool antigen were obtained in the study nor the control group. The results of this study demonstrate no causative link between HP and IHPS. A genetic basis has been implicated for IHPS. However, evidence does exist that IHPS is a condition acquired after birth and that an infective agent may be involved in the pathogenesis. Further studies are required to elucidate perinatal factors that may induce the expression of this condition in a genetically sensitive individual.