In this work, the photocatalytic degradation of aqueous microcystin-LR was studied using TiO(2) and ZnO as photocatalysts. The process was optimised and characterised at the bench scale (200 mL); both semiconductors exhibited a high degradation capacity at reaction times of 1 min (degradation greater than 95%). The transient species that were observed indicate that the degradation occurs via the multiple hydroxylation and elimination of the labile peptide residues of the molecule. When photocatalysis was applied in a continuous treatment system (20-50 L), the photocatalytic process exhibited a high degradation efficiency, which resulted in residual microcystin-LR concentrations that were less than 1 μg L(-1) (C(0)=5 μg L(-1)).