Lignites of the Thracian basin, the main coal potential of Bulgaria have been subjected to an extensive study, as their high sulphur content (3-7%) creates ecological problems during combustion. The aim of the present study was to examine the effect of desulphurization (three techniques, i.e. hydrothermal, t-BuONa and n-BuLi/TMEDA treatments) on biomarkers assemblage, as sulphur bridge cleavage could release covalently attached species or trapped molecules. Results of the chromatographic analysis of the aliphatic portions of the chloroform extracts from initial and treated lignites have pointed out that during desulphurization treatments coal organic matter was rearranged and smaller fragments became soluble. Some peculiarities were registered: alkane fraction of Maritza-Iztok treated by t-BuONa was strongly dominated by "even" carbon numbered n-alkanes, n-C-16, n-C-18 and n-C-20; in products of Elhovo lignite desulphurized by n-BuLi/TMEDA alkyl cyclopentanes were tentatively identified. After n-BuLi/TMEDA desulphurization, hopane distribution was largely affected in the case of the Maritza-Iztok sample: the higher homologues and pp dominance from C-29 to C-31 hopanes have disappeared; "geo hopanes" prevailance was registered;-18 alpha(H)-oleanane, 25-nor-17 alpha(H)21 beta(H)-hopane, C-29 and a suite of "non-hopanoid" C-30 triterpanes were observed. Our data have demonstrated the negligible steric protection of macromolecular structure in the case of low rank coals as far as covalently-bound species were characterized by higher degree of maturation compared to the easily extractable species.