A polymerase chain reaction for the specific detection of Helicobacter pylori was developed using a primer pair derived from the nucleotide sequence of the urease A gene of H pylori. Specific amplification of a 411 base pair DNA fragment from all strains of H pylori tested was achieved. Ten organisms were detected using the PCR and the technique permitted direct detection of H pylori in clinical biopsy samples. PCR will be useful for both prospective and retrospective investigation of the aetiology and epidemiology of H pylori associated disease.