Fusarium head blight (FHB), mainly caused by Fusarium graminearum species complex (FGSC) and also by other species of this genus, is one of the most destructive cereal diseases with high yield losses and mycotoxin contamination worldwide. The aim of this study was to identify Fusarium species, characterize their virulence factors such as trichothecene genotypes and cell wall degrading enzymes (CWDEs), and also investigate virulence of the isolates obtained from wheat plants with FHB symptoms in Golestan province of Iran. Among 41 isolates tested, 24 were F. graminearum sensu stricto (s.s.), six were F. proliferatum, four were F. culmorum, three isolates belonged to each of F. subglutinans and F. meridionale species and one isolate of F. asiaticum was identified. Among Fusarium isolates, the nivalenol (NIV) genotype could be found more frequently, followed by 3-acetyl deoxynivalenol (3-ADON) and 15-acetyl deoxynivalenol (15-ADON) genotypes. Production of trichothecenes in autoclaved rice cultures was analyzed by gas chromatography (GC) and confirmed by GC-MS. The mean levels of NIV, 3-ADON and 15-ADON produced by Fusarium spp. were 824, 665 and 622 mu g kg(-1), respectively. All Fusarium isolates were capable of producing CWDEs, mainly cellulase and xylanase. Lipase and pectinase activities appeared later and at less quantities. In overall, the isolates FH1 of F. graminearum and FH8 of F. proliferatum showed the maximum activity of CWDEs, which was correlated with high level of their virulence and aggressiveness on wheat. On the other hand, correlation was observed between the level and type of trichothecene produced by each isolate and its virulence on wheat. Virulence of trichothecene producing isolates was higher than that of non-trichothecene producing isolates. Our results suggested that CWDEs and trichothecenes, as virulence factors, have considerable roles on virulence and aggressiveness of the pathogen. This is the first report on the effect of trichothecenes and CWDEs on virulence and aggressiveness of Fusarium spp. associated with FHB disease in wheat growing regions of Iran.