Plants do not have the sophisticated immunoglobulin immune systems of vertibrates, instead they posses a series of stimuli based responses which defend against pathogentic attack. Part of these defence systems consists of a series of small cysteine rich, cationic proteins called defensins, which have specific antimicrbial acitivtys by a variety of differing mechanisms. In the proposed study we intend to examine the interaction of three plant defensins from differing protein familys with lipid monolayers, examining the mode and specificity of the proteins interaction with these model membranes at the sub-nanometer level. The proteins under study are Kalatan B1, a cyclotide with a wide range of biological activitys all related to its ability to form pores in pathogenic membranes. Rs-AFP2 a specific antifungal protein and ace-AMP1 a lipid transfer like protein from onion seed.