Abstract: The nested polymerase Chan reactiion ( nested-PC R)has been adopted to amplily the specific sequences of the macrophag e infectivity potentiator ( mip) gene of Legionella pneumophila ( Lp). 14 strains of Lp and 5 strains of non Legionella were tested. The results shown that only Lp amplified products had 649 bp specific DN A fragment. The sensitivity of amplification was about 100CFU /ml DAN of Lp. It was used to detect Legionella DN A in 17 blood specimens (including 6 specimens collected from patients with Legionnaires′disease). It was shown that the sensitivity of nestedPCK was significantly higher than that of serological and bacteriological culture method. The specificity were 100%, too. The above results suggest that nested-PCR may be a specific, sensititiv e and rapid technique for the diagnosis of Legionnaires disease.