The formation of furan as influenced by temperature and time of heating was studied in hazelnuts. Temperature was noted as the important processing parameter on the formation of furan in hazelnuts. The formation of furan was noticeably increased at temperatures exceeding 120 degrees C. Furan concentrations tended to increase linearly at 100 and 150 degrees C up to 60 min of heating. Detailed examination of the composition of different hazelnut varieties showed that certain precursors such as polyunsaturated fatty acids (linoleic acid), amino acids (threonine and alanine), and sugars (glucose) were present in hazelnut at amounts sufficient to generate significant amounts of furan upon heating. The composition of the lipid fraction in terms of relative percentages of fatty acids was relatively stable during heating at 150 degrees C for 30 min, but the concentrations of amino acids and sugars decreased significantly at the end of the heating period. This led to the conclusion that the Maillard reaction is possibly the primary mechanism responsible for the formation of furan in hazelnuts during heating.