A proposed kinetic model for elucidating the analyte pre-atomization losses in electrothermal atomic absorption spectrometry has been extended and developed further. The apparent activation energies, E(a)(loss), characterizing the process of analyte losses, have been derived from experimental data on absorbance and pre-treatment times at various pre-treatment temperatures for Sb, As, Pb and Sn, both in the absence and presence of a chemical modifier (20-mu-g of Mo(VI)). In the presence of a modifier, the maximum thermal treatment temperatures and the E(a)(loss) values were substantially increased and were of the same order, about 1300 K and 350 kJ mol-1, respectively, for the analytes As, Sb and Sn. For Pb, the corresponding values were 973 K and 60 kJ mol-1.