Major differences were found in the occurrence of glucosinolates in the leaves of different wild species of the Brassica oleracea (2n = 18) group. The distribution of glucosinolates supports the present classification with the exception of the inclusion of both Tunisian and Sardinian populations within B. insularis. The results also support the hypothesis of a polyphyletic origin of cultivated forms of B. oleracea from a number of wild species. In contrast, wild populations of B. rapa had very similar glucosinolate contents. Wild populations had a considerably higher total glucosinolate content than cultivars which may limit their usefulness in breeding programmes.