Puccinia graminis f. sp. tritici (Pgt), the basidiomycetous pathogen of wheat stem rust imposes up to 100% yield loss in disease epidemics. Host resistance to Pgt could be affected by emergence of new isolates virulent to wheat stem rust (Sr) resistance genes. Virulence diversity of Pgt races is assumed to be high in Iran, as a wheat center of origin. To identify virulence combinations on Sr genes, 123 Iranian Pgt isolates were individually inoculated on seedlings of 20 North American as well as 45 supplementary differential wheat genotypes. The Stakman et al. 0-4 scale was used for visual evaluation of infection types (IT) on leaves at 14 days post inoculation (dpi). Results showed that the Sr resistance genes, Sr5, Sr6, Sr7a, Sr7b, Sr8a, Sr8b, Sr9a, Sr9b, Sr9d, Sr9e, Sr9g, Sr10, Sr11, Sr12, Sr15, Sr16, Sr17, Sr18, Sr19, Sr20, Sr21, Sr23, Sr30, Sr34, Sr36, Sr38, SrTmp and SrMcN were ineffective to many isolates tested. In contrast, Sr24 and Sr26 conferred resistance to all Iranian Pgt races. Sr31 was merely ineffective against few isolates identified as the race TTKSK and its new variant, TTKTK. Our results demonstrated ineffectiveness of Sr14, Sr28, Sr29 and Sr37 to all Iranian Pgt races tested. Moreover, this paper is the first report of virulence to Sr13, Sr25 and Sr27 in Iran caused by the new variants of TKTTF and TTTTF, and by the new race, PTRTF at frequencies of 91%, 61% and 5%, respectively. New virulence, identified on previously effective Sr genes, should be considered as a warning in wheat breeding programs for stem rust resistance in Iran.