Nerolidyl pyrophosphate has been established as the biosynthetic precursor to cadalene-type sesquiterpenoids such as gossypol. Using [1,2-(13)C(2)] acetate, we established that trans-nerolidyl pyrophosphate is the biosynthetic precursor of gossypol and related phytoalexins in chilled cotton (Gossypium arboreum) radicals.