The fibers of the green lint mutant of cotton (Gossypium hirsutum L.) contain large amounts of wax and are suberized. More than 96% of the bifunctional aliphatic suberin monomers ([alpha],[omega]-alkanedioic acids and [omega]-hydroxyalkanoic acids) have chain lengths of C22 and C24 in green cotton fiber suberin. In fibers grown in the presence of S-ethyl-N,N-dipropylthiocarbamate (EPTC), a specific inhibitor of the endoplasmic reticulum-associated fatty acid elongases, the aliphatic suberin monomers were shortened to chain lengths of C16 and C18. Whereas the amounts of most suberin monomers were not negatively affected by the inhibitor treatment, the amounts of [alpha],[omega]-alkanedioic acids and of glycerol were reduced by more than 80%. Analysis in the transmission electron microscope showed a reduction in suberin content after EPTC treatment. The suberin layers were discontinuous and consisted of fewer lamellae than in the controls. A small proportion (up to 22%) of the electron-translucent suberin lamellae were thinner after EPTC treatment, probably because of the shortening of the aliphatic suberin monomers. A larger proportion of the electron-translucent lamellae were thicker than the lamellae in the controls. Possible explanations for this observation are discussed.