A cDNA library from tobacco inoculated withRhizoctonia solaniwas con-structed, and several cDNA fragments were identified by differential hybridization screening. One cDNA clone that was dramatically repressed, NtKTI1, was confirmed as a member of the Kunitz plant proteinase inhibi-tor family. RT-PCR analysis revealed that NtKTI1was constitutively expressed throughout the whole plant and preferentially expressed in the roots and stems.