The feasibility of perchloroethylene (PCE) biodegradation using hybrid aerobic/anaerobic microcosms was investigated. Four main factors were evaluated in batch studies; the type of the electron donor, the nature of the inoculum, the effect of different concentrations of electron donor, and the effect of addition of different concentrations of oxygen. Results from these studies showed that; glucose was the best electron donor for PCE degradation, serum bottles seeded with acclimated biomass performed better than those seeded with the unacclimated biomass, glucose in excess did not improve PCE degradation, and the addition of pure oxygen significantly enhanced degradation. It was observed that serum bottles with acclimated sludge receiving oxygen achieved complete mineralisation of PCE to ethylene with mineralisation rates of 0.27 mg L-1 mg cells' h(-1). Following these results a membrane-aerated biofilm reactor (MABR) was constructed, and the batch degradation of 5.5 mg L-1 of PCE was followed for 44 days and PCE was completely removed from the system. The appearance of intermediate compounds proved that PCE was degraded, but not completely stripped out from the system. Degradation was not complete as some bio-products were still found in the effluent, but there was no accumulation of a particular intermediate compound. The PCE removal rate observed in this MABR was 0.24 mg L(-1)h(-1). During the study on the effect of adding different concentrations of oxygen, a mass balance based on chloride in the bottles revealed that, 92-95% of the PCE could be accounted for, while only 60-65% of the PCE fed in the reactor could be accounted for as chloride. The MABR developed here may prove to have considerable potential in treating, wastewater containing a variety of refractory organics such as PCE. (c) 2006 Society of Chemical Industry.