Our longterm studies of Verticillium wilt resistance have yielded a theoretical explanation of the nature of resistance in the Gossypium barbadense - Verticillium dahliae model system. The localized resistance response in stem xylem is effected by the sequential, integrated action of anatomical and biochemical factors. These studies have evolved over the past 15 years. Desoxyhemigossypol has been identified as the major phytoalexin in the G. barbadense resistance response. Histochemistry was of critical importance in the integration of anatomical, classical biochemical and toxicology data to achieve a theoretical explanation of Verticillium wilt resistance.