The polymerase chain reaction was used for the detection of Helicobacter pylori from subgingival plaque in 336 periodontitis patients. A pair of primers derived from the H. pylori urease gene A served to amplify a targeted 411-bp fragment of genomic DNA. This technique permitted the detection of as few as 60 H. pylori cells. Paper point samples from 3 deep periodontal pockets per patient were immersed in 1 ml of phosphate-buffered saline or distilled water, DNA was solubilized by detergent/protease method, 3.7 microliters or 37 microliters of lysate supernatant was used as template, and the amplification product was analyzed in 1% agarose gel containing ethidium bromide. Each experiment included purified DNA and cell lysate of H. pylori as positive controls. The presence of bacteria in the sample was verified by a primer pair common to prokaryote 16S rRNA. The present study did not reveal the specific polymerase chain reaction amplification product characteristic of H. pylori. We conclude that periodontal pockets do not constitute a natural reservoir for H. pylori.