Apple fruits and grapevine leaves were inoculated with four wild-type strains of Botrytis cinerea. Two types of symptoms were observed on apple, firm or soft rot. Extracts from infected tissues were analysed for polygalacturonase (PG) and pectin methylesterase (PME) isozyme profiles. They showed that different specific PG isozymes occur in grapevine leaves and in soft rot on apple fruit. PG and PME profiles were also studied in genetic transformants altered in their colonization ability and/or the type of rot that they caused on apple fruit. No PG activity was found in apples infected by firm-rotting wild-type strains or transformants, whereas two neutral PG isozymes (pIs 7.3 and 7.6) were expressed in soft-rotting strains. No association was found between the production of these PG isozymes and the colonization level. The PME patterns were not correlated with the rotting type nor the colonization level. In vitro, firm-rotting strains and transformants showed no PG activity in glucose medium whereas soft-rotting ones produced several PG isozymes. In polygalacturonic acid cultures, all strains and transformants produced a single, common acidic isozyme. Unlike PG, no variation in the PME isozyme patterns in vitro could be correlated with the culture substrate on apple or the rotting type. The variation in pectinase profiles between in vitro and in planta contexts and the role of PGs in B. cinerea pathogenicity on apple fruit is discussed. We suggest that neutral PG isozymes are involved in the soft-rotting type on apple fruit.