Streptococcus pyogenes causes a variety of common human diseases, including pharyngitis, scarlet fever and impetigo. Nevertheless, the past decades have witnessed a worldwide resurgence in invasive disease and streptococcal toxic shock syndrome (STSS). The objective of the present study is to evaluate the genetic diversity, virulence gene distribution (spe, sme and ssa genes) and susceptibility pattern of 10 S. pyogenes isolates causing invasive disease and STSS. The isolates were recovered from blood cultures of hospitalized patients at Hospital Santamarina and Nueva Clínica Chacabuco, Tandil, Buenos Aires, Argentina between 12/2000-04/2005. Two pulse field gel electrophoretic patterns predominated. The most frequent one included 5 characteristic isolates of emm1-T1 type, toxin gene profile speA, speB, speF, speG and smeZ. The second pattern included 2 characteristic isolates of emm3-TNT type (speB, speF, speG). The other 3 isolates corresponded to types emm49-TNT (speB, speC, speF, speG), emm75-T25 (speB, speF, speG) and emm83-TNT (speB, speF, speG, ssa, smeZ). All isolates were susceptible to penicillin, cefotaxime, erythromycin, clindamycin, chloramphenicol, tetracycline and rifampicin. The data from the present study demonstrated genetic diversity among the strains. Types emm1 and emm3 were prevalent in invasive disease. The empirical treatment with the combination of penicillin and clindamicin is still valid.