In 2002, the Romanian National Reference Laboratory was invited to join the Strep-EURO project to study invasive Streptococcus pyogenes infections. During 2003 and, a total of 33 isolates recovered from invasive disease were received from eight Romanian counties. For comparison, 102 isolates from non-invasive disease, as well as a collection of 12 old invasive strains (isolated between 1967 and 1980) were included. All isolates were characterized by several methods: T and emm typing, presence of the fibronectin-binding protein F1 gene (prtF1), serum opacity factor (sof), and superantigen (SAg) genes (speA, speB, speC, speF, speG, speH, ssa and smeZ). The recent invasive isolates exhibited 19 emm-types, of which emm1, emm81, emm76, emm49 and emm78 covered 57 % of the strains. Furthermore, multilocus sequence typing analysis revealed nine new sequence types, corresponding to emm types 1, 12, 49, 81, 92, 100, 106 and 119. The non-invasive isolates comprised 24 different emm types with a predominance of emm1 and 12; the old invasive strains were of eight emm types, of which four were unique for this group. All isolates harboured speB and speF; smeZ was detected in all invasive strains, except for the emm49 and emm81 isolates. The majority of isolates from carriers, and patients with pharyngitis were prtF1 positive, most of these (14 strains) being emm12. High tetracycline resistance rates were noted among both invasive and control isolates (54 % and 35 %, respectively), whereas macrolide resistance rates were low (3 % and 5 %, respectively). Active and continuing surveillance is required to provide an accurate assessment of the disease burden and to provide epidemiological data on the character of isolates in Romania. INTRODUCTIONGroup A streptococci (GAS, Streptococcus pyogenes) is one of the major human pathogens (Carapetis et al., 2005), giving rise to various suppurative complications of infection, e.g. acute throat and skin infections, as well as severe systemic disease such as cellulitis, puerperal sepsis, pneumonia, septicaemia, necrotizing fasciitis (NF) and streptococcal toxic shock syndrome (STSS) (Cunningham, 2000). In addition, GAS infections can give rise to nonsuppurative sequelae, such as acute rheumatic fever and acute glomerulonephritis (Cunningham, 2000).The heterogeneity exhibited by the N terminus of the Mprotein, the major GAS virulence factor (Bisno et al., 2003), is used in the M-serotyping technique (Lancefield, 1962). The emm gene (encoding the M-protein) is successfully targeted in sequence typing (Johnson et al., 2006). Another GAS surface protein, T-protein, was used as a basis for a crude, but widely used subdivision of strains (Moody et al., 1965). The variable presence of an apoproteinase serum opacity factor (SOF) enabled separation of Abbreviations: CSF, cerebrospinal fluid; GAS, group A streptoccocci; iGAS, invasive group A streptococci; MLST, multilocus sequence typing; NF, necrotizing fasciitis; PFGE, pulsed-field gel electrophoresis; RFLP, restriction fragment length polymorphis...