A microalga (VT-1) was isolated from pentachlorophenol (PCP) treated water. Its growth and PCP tolerance was compared with two known strains of Chlorella and it was found to be more tolerant with an IC50 (24-25 mg dm(-3)) value twice that of C. vulgaris. The ability of VT-1 to degrade PCP was tested using uniformly labelled PCP, and (CO2)-C-14 was released, indicating mineralisation. (CO2)-C-14 was not released in the presence of the other microalgae and only occurred in the light. Release was also stimulated by the presence of glucose in the light.