Detection of M.leprae by peR provides a tool for identification of organisms inrnclinical specimens. Genomic DNA and RNA were isolated using commerciallyrnobtained extracting solutions (DNA STAT 60Thl and RNA STAT 60ThIrn). RNArnwas reverse transcribed to make cDNA and both genomic DNA and cDNA werernsubjected to PCR amplification. Products were electrophoresed through agaroserngels, stained with ethidium bromide, blotted onto nylon membranes',hybridizedrnwith a 16S rRNA oligonucleotide probe and subjected to non-radioactiverndetection. Several sets of 16S rRNA primers were investigated. Of these, onernset of primers (P2 and P3) en = bp # 68-90 and P3 = bp # 218-239) wasrnconfirmed to be specific for M.leprae by testing its ability to amplify a panel ofrn28 potentially cross-reacting species of mycobacteria, 8 related non-mycobacterialrnisolates and 2 nasopharyngeal commensal organisms. In addition no amplificationrnwas observed when skin biopsies from normal individuals or patients with skinrndiseases other than leprosy were tested. Another set of primers (PI and P3)rn(PI = bp # 9-28 and P3= bp # 218-239) was genus-specific. After optimizationrnof the peR condition. the sensitivity of the system was assessed using M.lepraespecificrnprimers and the detection limit was 23 bacteria. This technique,rntherefore. appears to meet the criteria of sensitivity and specificity and may servernas a useful tool for the diagnosis of leprosy. By examining a limited number ofrntissues from leprosy patients, we were able to detect peR signals in all MB (n=rn5) and in 89 % (n= 9) of PB patients. We also quantitated numbers ofrnorganisms in these specimens by comparing the density of the peR signal ofrnsamples on hybridized Southern blots to that of serial dilutions of known numberrnof organisms.