Many plants possess antimicrobial peptides (AMP) constitutively expressed or induced after infection. These families of peptides include four cysteine-type peptides: hevein and knottin-type peptides, lipid transfer proteins, plant defensins and thionins. Plant AMP are basic, cystein-rich peptides with molecular masses of approximately 5 kDa. They are mainly identified in perypheral cell layer of plants. These peptides may have an important role to play in the protection of plants from microbial infection, and they might prove to be useful tools for the genetic engineering of fungal and other patogen resistance in transgenic plants. Plant defensins family show very limited sequence conservation.