AbstractÐThe site occupancies of V, Cr, Mn, Fe, Ni, Zr, Nb, Mo, Ta, Ga and Sn (1±5 at.%) in TiAl alloys with dierent compositions, and in Ti 3 Al with the compositions of Ti±26 at.%Al±(1±2 at.%)X, were measured by the atom location channelling enhanced microanalysis (ALCHEMI) method. For TiAl alloys, the results show that Zr, Nb and Ta atoms invariably occupy Ti sites, while Fe, Ni, Ga and Sn atoms occupy Al sites, the alloy composition having no signi®cant in¯uence on their site preference. By contrast, the site preference of V, Cr, and Mn changes considerably with alloy composition (the Ti/Al ratio in particular), the probability of these elements substituting for Ti decreasing in the above order. For quaternary Ti±Al±V±Cr alloys, the site occupancies of V and Cr do not show much mutual in¯uence. In general, with increasing atomic number, elements in the same period show increasing tendency to substitute for Al, as is the tendency to substitute for Ti for elements in the same group of the periodic table. For Ti 3 Al alloys, Ga and Sn atoms occupy Al sites, while V, Cr, Mn, Zr, Nb, Mo and Ta atoms occupy Ti sites, the site preference of V, Cr, Mn and Mo in TiAl alloys being dierent from that in Ti 3 Al. The experimental results are interpreted in terms of a Bragg±Williams-type model and bond-order data obtained from electronic structure calculation. Qualitative agreement between the model and measurements is reached.