HMGR activity and D-cadinene cyclase are induced more rapidly in resistant Seabrook Sea Island (SBSI) cotton (Gossypium barbadense) than in susceptible Rowden (G. hirsutum). Similarly the concentrations of the important phytoalexin desoxyhemigossypol and of total phytoalexins increase quicker in SBSI than in Rowden. These observations agree with the hypothesis that induction of phytoalexins is an essential element in the resistance response in cotton.