The energetic and structural characteristics of atomic ordering processes in Fe-0.5(Al1-nXn)(0.5) intermetallics have been qualitatively analyzed based on the statistico-thermodynamical theory of ordering by means of a quasi-chemical method combined with electronic theory in the pseudopotential approximation. The effects of ternary impurities on order-disorder phase transformation temperature and the characteristics of atomic short-range order in Fe-Al type intermetallics have been calculated. Impurity elements in Fe-0.5(Al1-nXn)(0.5) where X = Ni, Co, Mn, Cr, Ti, Si, Zr, Hf, Nb, Ta, Re, Mo or W, are considered up to 1 at.% concentration. The results of the calculation indicate that the impurity elements, X, with regard to their lattice site occupancy characteristics (SRO) can be divided into two groups; X-1 = Ni, Co, Mn or Cr element atoms substitute mainly for Al sublattice sites, whereas Xii = Ti, Si, Zr, Hf, Nb, Ta, Re, Mo or W element atoms substitute preferentially for Fe sublattice sites in Fe-0.5(Al1-nXn)(0.5) intermetallics. It has been found that the absolute values of partial ordering energies of the WAl-X (R-1) and WFe-X(R-1) have a profound effect on the order-disorder transition temperature of Fe-0.5(Al1-nXn)(0.5) alloys that would either increase or remain unchanged depending on the type and content of the ternary substitutional alloying elements. The impurities X = Zr, Hf, Nb, Ta, Re, Mo or W which are preferentially distributed Fe sublattice sites are more effective in increasing order-disorder transition temperature in Fe-Al(B2) intermetallics. The results of the present calculation are in good qualitative agreement with experimental observation for most of the third component impurity elements X in Fe-0.5(Al1-nXn)(0.5) intermetallics. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.