Helicobacter pylori is an organism thought to play an important causative role in gastritis and peptic ulcer diseases. We have designed an RNA dot blot assay for the detection of H. pylori, using as probe a synthetic oligonucleotide complementary to its 16S rRNA. We have also used oligonucleotide primers, complementary to conserved sequences within bacterial ribosomal 16S genes, to amplify a H. pylori ribosomal 16S DNA fragment via the polymerase chain reaction (PCR). After determining the DNA sequence of this amplified H. pylori fragment, primers were designed for specific PCR amplification of H. pylori ribosomal 16S DNA sequences. Samples from clinical endoscopic biopsies were PCR amplified with universal 16S ribosomal primers to detect the presence of bacteria and with H. pylori-specific primers to uniquely detect H. pylori. Finally, by comparing the H. pylori-specific PCR assay to commonly used diagnostic tests, we demonstrate that the molecular technique of PCR amplification shows promising applications for the clinical detection of H. pylori.