Benzothiazoles (BTs) and benzotriazoles (BTAs) are aromatic heterocyclic compounds which have been detected in aquatic environment, soil and wastewater treatment plants. These compounds demonstrate toxicity towards activated sludge microorganisms, as well as towards higher organisms, thus they are regarded as a threat to biological wastewater treatment. Studies performed on activated sludge as a mixed culture show that the transformation of BTs and BTAs is possible, in some cases also biologically. In this experiment it was revealed that BTA is degraded more easily and more efficiently than BT by activated sludge isolates. The decrease in the concentration of these compounds was not drastic but none of the isolated cultures were enriched or prepared to such a process performance. As a confirmation of these studies the next step in the analysis should be the culture pre-treatment (such as enrichment) or cometabolic degradation together with a more easily degradable carbon source.