Glucoraphanin is a potentially valuable plant compound that has shown efficacy in the treatment of hypertension and the removal of carcinogens in animals. Our recent work determined the optimum extraction conditions for the recovery of high amounts of glucoraphanin from the noxious weed Cardaria draba in a single-staged batch extractor. In this study, a multiple contact, countercurrent flow extraction process was used to achieve further improvements in glucoraphanin recovery. The yield increased by 1.5 times when compared with a single, batch contact extraction. A three-stage process was sufficient to extract over 90% of the glucoraphanin from C draba at a dry weight plant loading of 50 g dm(-3). The experimental results at several solids loadings agreed with the leaching theory and the theoretical model was used to predict the number of stages needed to extract all the glucoraphanin from C draba at high solids loadings. Finally the efficacy and toxicity of the crude glucoraphanin extracts were tested using hepatoma cells. The efficacy was found to be much higher than single-stage extracts, confirming that cell efficacy is related to the increased quantity of glucoraphanin extracted due to countercurrent operation. The crude extract demonstrated negligible acute toxicity to the hepatoma cells. (c) 2005 Society of Chemical Industry.