Glucosinolates constitute a well-defined group of secondary plant metabolites in cruciferous plants. They occur especially in brassica vegetables, which represent a major part of the human diet. Glucosinolates undergo hydrolysis, catalysed by an endogenous plant enzyme, known as myrosinase, into a range of biological active compounds. Some compounds, for example isothiocyanates, show an anticarcinogenic action by inducing phase II biotransformation enzyme activity (Jongen, Proc. Nutr. Soc. 1996; 55: 433-446). Processing of brassica vegetables influences glucosinolate degradation and therefore the biological activity. We investigate the effects of processing conditions on glucosinolates and their breakdown products. Besides measurement of concentrations also the biological activity of these compounds will be analysed.