The cationic antimicrobial peptides, indolicidins and polyphemusins, have shown activity against animal pathogenic viruses. The aim of this work was to evaluate the efficacy of these peptides for engineering plants with a broad-spectrum disease resistance, including viral diseases. TTC, Evan's blue and phytotoxicity assays showed low cytotoxicity of indolicidin and polyphemusin variants (10R, 11R and PV5) on tobacco leaf discs, protoplasts and plantlets. In vitro assays using these variants showed a broad-spectrum activity against plant pathogenic bacteria, fungi and viruses. An assessment of in planta activity was performed by expressing these cationic peptides in transgenic tobacco (Nicotiana tabacum var Xanthi). The disease assays using detached leaves from transgenic tobacco plants showed a broad-spectrum disease resistance against bacteria, fungi and 'TMV. Further work is needed on optimization of expression of these peptides and their combinations for successful application of this approach under greenhouse and field conditions.