This paper presents methodology of measurement and the results of investigations on detection of mechanical damage to apples with the use of thermography. Three varieties of apples were studied: Jonagold, Ligol and Gloster. Apples were bruised by dropping them from 0.25 m onto a smooth, ceramic surface. Before and after the measurement of radiation temperature, apples were stored at the temperature of 1.5°C. Thermal images of apple surface with bruises were obtained with the use of AGEMA 880 LWB system during 12-minute session of heating of apples at ambient temperature of 25°C. In each thermogram two surfaces were selected, first covering the bruised surface of the fruit and second, the surface of sound tissue. The obtained courses of temperature changes of both surfaces during the heating process showed, for all the studied varieties, the occurrence of temperature differences between bruised and sound parts in the range of 0.5-1.5°C. The highest differences of radiation temperature were noticed for Jonagold variety and the lowest for Gloster variety, which is determined by the highest differences in firmness between these two varieties.