A polygalacturonase-inhibiting protein (PGIP) has been purified from immature raspberry fruits. The wall-bound protein with a MI of 38.5 kDa and pl residing above pH 10.0 acts specifically as a non-competitive inhibitor of endopolygalacturonases (PGs) produced by Botrytis cinerea. These fungal PGs are thought to be important in pathogenesis and the onset of aggressive grey mould. The inhibitor was present at high concentration in the green immature fruits, but declined rapidly with ripening of drupelets, concomitantly with the increase in susceptibility of fruits to grey mould as determined by wound-inoculation with the pathogen. The PGIP gene from raspberry is being cloned, with the ultimate objective of using recombinant DNA technology to enhance the expression of the gene in fully ripe fruits. By these means it may be possible to improve substantially the grey mould resistance of fruits of existing and future raspberry cultivars.