The aim of the study was to evaluate polycyclic aromatic hydrocarbons (PAHs) removal during co-fermentation of sewage sludge and organic fraction of municipal solid waste under nitrate and sulphate reducing conditions. Samples were incubated at 37 degrees C for 20 d. Two series of experiments were running simultaneously to evaluate biodegradation and abiotic loses of PAHs. To arrest biological activity cyanides were added. As required for nitrate and sulphate reduction NaNO3 and Na2SO4 were introduced. PAHs were determined before and after incubation. The results of PAHs degradation under various reducing conditions were compared with a blank assay, where no additional electron acceptors were added. PAHs total concentration in raw mixtures was equal to 446 mu g kg(d.m.)(-1) The most abundant congeners were naphtalene and fluorene. Statistically significant decrease of fluorene and phenanthrene was observed both under nitrate and sulphate reducing conditions. The removal mechanism was concluded to be abiotic. Under nitrate reducing conditions anthracene, fluoranthene and pyrene removal was also stated. In blank assay statistically significant decrease of fluorene concentration was only observed. As a result of the investigations it can be stated that redox conditions had effect on PAHs fates. Further investigations concerning mechanisms of PAHs removal under various redox conditions are however required.