The effect of Verticillium dahliae 277 on the induction in Gossypium cell suspension cultures of sesquiterpene Aldehydes, possible phytoalexins, was investigated. The moderately resistant G. arboreum Nankin cell cultures were able to increase sesquiterpene aldehyde formation 39 fold compared to a 12 fold increase in the susceptible G. hirsutum Tamcot Sp 37 cultures. Mainly hemigossypol, smaller amounts of gossypol and an unknown compound was synthesized in the cell suspension cultures. With exception of the unknown compound, the pattern was similar to the compounds synthesized in infected cotton stem tissue. Of 25 random cells growing in suspensions, 4 were diploid, 6 tetraploid, 4 hexaploid and 11 intermediate levels. A glycoprotein was isolated from V. dahliae 277 conidia and from medium in which V. dahliae had been growing. This glycoprotein acts as an elicitor for the induction of sesquiterpene aldehyde formation when added to cotton cell suspension cultures.