The aim of the present work is to study order-disorder transformation in some alloys of the Fe-Al system ( with 9.8, 21.5 and 25 at.% Al). The synthesis and the analysis of numerous and interesting results obtained by dilatometric and calorimetric analysis have allowed us to assert that the ordering reaction is a rapid process and that long ageing at 300degreesC leads to an increase in the degree of ordering of the DO3 phase. (C) 2004 Kluwer Academic Publishers.