This proposal seeks to investigate a class of synthetic membrane-active biopolymers which have been developed as potential drug-delivery agents. These polymers have shown pH- and concentration-dependendent binding and permeabilisation of phospholipid membranes, but their mechanisms of action are not well understood. The complex polymer phospholipid interactions will be modelled using combinations of data from d-labelled polymer and lipid, and molecular structure based co-refined modelling. This modelling will directly compare neutron reflectometry results with the results of Monte Carlo simluations that predict a distribution of polymer throughout the bilayer, dependent on the hydrophobicity and type of sidechain found on the biopolymer. These measurements will be correlated with electrochemical measurements recently published which suggest reversible alteration of membrane properties.