The Scientific Panel on Food Additives, Flavourings, Processing Aids and Materials in Contact with Food (the Panel) is asked to advise the Commission on the implications for human health of chemically defined flavouring substances used in or on foodstuffs in the Member States. In particular, the Scientific Panel is asked to evaluate 20 flavouring substances in the Flavouring Group Evaluation 17, Revision 1 (FGE.17Rev1), using the procedure as referred to in the Commission Regulation (EC) No 1565/2000. These 20 flavouring substances belong to chemical group 24 of Annex I of the Commission Regulation (EC) No 1565/2000. The present Flavouring Group Evaluation (FGE) deals with 20 pyrazine derivatives. Three of these derivatives are quinoxalines. Five of the 20 flavouring substances possess a chiral centre. For two of these substances the stereoisomeric composition has not been specified. Sixteen of the flavouring substances are classified into structural class II and four are classified into structural class III.Nineteen of the flavouring substances in the present group have been reported to occur naturally in a wide range of food items.