We will use specular and off-specular neutron reflectivity to provide a structural mechanism for the way in which the amphipathic peptide pinholin controls bacterial cell lysis and hence infection of bacteria by phage lambda. In vivo studies have suggested a mechanism whereby pinholin is initially uniformly distributed across the inner leaflet of the inner bacterial membrane until a critical coverage is reached at which point they redistribute into 100 nm diameter rafts and then collectively rearrange into a series of 2 nm channel diameter heptameric transmebrane pores. Contrast variation and specular reflectivity from floating bilayer will allow peptide pores (high solvent penetration) to be distinguished from uniform peptide distribution. Off-specular measurements will allow this transition to be correlated to raft size. The combination will enable the pore size to be measured.