The microstructure of raw and roasted hazelnuts was investigated with light microscopy (LM). Tissue sections were fixed chemically using a mixture of formaldehyde, glutaraldehyde and buffer. Polyester was used as a resin. Thin sections were prepared by using a grinding method. Thermal changes in the microstructure developed gradually with increasing air temperature, air velocity and roasting time. Roasting led to some degree of cell wall separation and intercellular spaces, partial disruption of cytoplasmic network, swollen and aggregated protein bodies. These changes were observed in the microstructure of extremely liked quality of hazelnuts (roasted at 165 degreesC, 1 m/s. 25 min.). Due to the increase in the volume of intercellular spaces, crispness and crunchiness of roasted hazelnuts were increased. (C) 2002 Elsevier Science Ltd. All rights reserved.