Glucosinolates are found naturally in cruciferous plants, such as brassica vegetables, which are important in the human diet. Glucosinolates are readily converted into a range of physiologically active compounds by hydrolysis under the influence of an endogenous thioglucosidase, which becomes active when plant cells are disrupted. Cruciferous vegetables are eaten raw, they are also consumed in the processed form. The influence of processing conditions on glucosinolate degradation and on the type and levels of the reaction products formed is reviewed.