Eight Mycosphaerella graminicola isolates were investigated for correlations between pathogenicity and the in vitro production of cell wall-degrading enzymes. Isolate pathogenicity was evaluated in terms of lesion and production of pycnidia in wheat leaves. Additionally, the isolates were compared over time for their ability to produce in vitro significant levels of xylanase (EC 3·2·1·8), β-xylosidase (EC 3·2·1·37), β-1,3-glucanase (EC 3·2·1·6), cellulose (EC 3·2·1·4) and polygalacturonase (EC 3·2·1·15) activities when grown in a liquid medium. Correlation tests and principal component analysis revealed a significant correlation between the in vitro production of xylanase and pectinase and pathogenicity components. Xylanase was correlated to necrosis frequency (r = 0·795), β-xylosidase was correlated to the mean of the lesion length (r = −0·787), whereas polygalacturonase was correlated to the time when 50% of the leaves contained a lesion (r = 0·776), the lesion frequency (r = 0·646) and the time when 50% of the leaves showed pycnidia (r = −0·711). The results suggest that these two groups of cell wall-degrading enzymes are therefore likely to be key determinants of pathogenicity in M. graminicola.