Polygalacturonase-inhibiting proteins (PGIPs) are plant defence molecules inhibiting the activity of fungal endo-polygalacturonases (endo-PGs). We found that soybean and bean PGIPs inhibited the endo-PG activity produced by the isolate FC-10 of Fusarium moniliforme but not the enzyme activity produced by the isolate PD of F. moniliforme. The bean PGIP proved to be ineffective against all the PG isoforms produced by the PD isolate. Deduced amino acid sequence comparison between PGs from PD, FC-10 and 62264 isolates identified the structural regions of the enzyme possibly related to its resistance to PGIP inhibition. These include one region at the N-terminal portion of the enzyme and a few single amino acid substitutions along the entire sequence, two of which surrounding the active site.