The mechanism of general anaesthetic action is poorly understood despite their widespread use. It is hoped that investigating the interaction of anaesthetics with lipid bilayers will help develop our understanding of how they work. We have recently demonstrated that we can resolve both the position of the anaesthetic molecule and the resultant affect on the lipid bilayer using neutron reflection from simple SAM supported floating membranes. In this proposal we plan to consider a hypothesis that the degree of saturation within the bilayer tails should be directly correlated to the affinity of the membrane to anaesthetic molecules due to its ability to freely rearrange. Therefore, we will study partially and fully unsaturated lipid bilayers exposed to the anaesthetic molecule at 37C; and observe the changes that occur.