Tehran University of Medical Sciences Journal of Medical Bacteriology 2251-8649 1 1-2 2015 10 12 38 45 EN Seyyed Saeed Eshraghi Section Microbiology, Department Pathobiology, School of Public Health, Tehran University of Medical Sciences, Tehran, IR Iran. 2015 10 12 2015 10 12 Identification  of clinically  significant  Nocardia  species  is essential  for the definitive diagnosis, predict antimicrobial susceptibility, epidemiological purposes,  and  for  an  effective  treatment.   Conventional   identification   of Nocardia species in routine medical laboratories which is based on phenotypic (cellular morphology, colonial characteristics), biochemical and enzymatic profiles, and chemotaxonomic characteristics is often laborious, and time- consuming.  The  procedure  requires  expertise,  and  newer  species  can  be difficult to differentiate with accuracy from other related species. Alternative methods  of identification,  such as high performance  liquid chromatography (HPLC) and molecular  biology techniques  allow a better characterization  of species.  The  taxonomy  of  the  genus  Nocardia  has  been  dramatically  been revised  during  the  last  decade  and  more  than  30  valid  human  clinical significance  species  of Nocardia  have been reported.  The use of molecular approaches, including 16S rRNA gene sequencing, restriction fragment length polymorphism (RFLP) or PCR restriction endonuclease analysis has been the focus  of  recent  investigations  to distinguish  the  isolates  of  Nocardia  from other  actinomycetes  genera.  The  methods  have  revolutionized the characterization  of the Nocardiae by providing rapid, sensitive, and accurate identification  procedures. The present  review  describes the currently  known medically important pathogenic species of Nocardia.   https://jmb.tums.ac.ir/index.php/jmb/article/view/11 https://jmb.tums.ac.ir/index.php/jmb/article/download/11/9