Polypeptides from the apple pulp of Smoothee Golden Delicious and White Renete apples were resolved by 1-D denaturing sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). According to the electropherograms, there were lower concentrations of 88, 74, 70.6 and 47.5-42kDa proteins in bitter pit spots. Proteins weighing 30 and 26kDa were rare in sound pulp but frequently appeared in pits and adjacent tissue. Finally, a novel 18kDa protein was found in bitter pit spots in both varieties, and also in chemically induced corky lesions either by magnesium infiltration or ammonium oxalate cortical injections. The available data suggested that the novel protein might be an inhibitor of pectinmethylesterase, a small heat stress protein (smHSP) or a product of the Ypr-10 gene family identified with ‘Mal d 1’, the main allergen of apples. To elucidate the possible smHSP nature of the 18kDa, a set of apples were heated at 40°C for 20h, developing this protein in both the oxidised tissue and in the adjacent.