In this study, harpin protein was applied to the peppers (Capsicum annuum L. var. cvs. 'Dernre', 'Yalova Charleston' and 'Sari Sivri') grown under natural conditions. These plants were subjected to artificial inoculation with Botrytis cinerea, which causes fruit spoilage in peppers. Changes in vegetative growth, total chlorophyll content in leaves, leaf colour and percentage of rotten fruits were determined after treatments. The number of leaves per plant value was quite low in all cultivars and the plant height value was low only in cv. 'Sari Sivri' treated with B. cinerea. Values obtained from vegetative growth parameters in the plants subjected to harpin protein + B. cinerea treatment were only higher than B. cinerea treatment. Leaf chlorophyll values exhibited significant decline in the plants subjected to B. cinerea treatment in all cultivars. However, the chlorophyll content in the plants subjected to harpin protein + B. cinerea treatment was low. The colour values obtained from leaves supported the chlorophyll findings. Fruit spoilage percentages were lower in the fruits picked from the plants of harpin protein + B. cinerea treatment compared with those picked from the plants only subjected to B. cinerea treatment. (c) 2006 Elsevier B.V. All rights reserved.