<正> A nested polymerase chain reaction（N-PCR）for the spegific detection of Helicobacterpylori（H.pylori）was developed with two primer pairs（nested primers）derived from ureasegene A of H.pylori.The N-PCR was used to detect 21 different samples of H.pylori including20 clinical isolates and 1 reference strain NCTC 14126

but it was negative for other bacterialspecies

showing the N-PCR assay to be 100% specific.Tenfold serial dilution experiments re-vealed the detection of as little as 0.1 fg of H.pylori DNA by N-PCR.To evaluate the PCR as-say for clinical samples

gastric biopsies were tested with N-PCR

and the results were comparedwith those of culture

urease test and histologic examination（reference standard

RS）.In 30biopsy specimens

H.pylori DNA sequences were detected by PCR in all of 20（100%）positivetissue and none of the 10 negative tissues.PCR is a specific and sensitive method that can detectthe presence of H.pylori without the need for culture and would have significant importance di-agnostically and epidemiologically.