The oxidation of membrane lipids by reactive Oxygen Species, ROS, is implicated in cell apoptosis, cancer and ageing. We wish to study the degradation by a single ROS species, singlet oxygen, of a bilayer composed of the unsaturated lipid, DOPC. DOPC contains a reactive double bond midway along the lipid tail and we wish to determine whether the damaged, shortened lipids, leave the interface immediately or if attack by singlet oxygen initially leads to a thinner bilayer structure. Our previous successful experiments at Isis revealed that when a saturated DPPC lipid bilayer was attached by singlet oxygen the amount of DPPC at the interface decreased steady but the thickness did not ie material was lost in patches, rather than by a gradual thinning of the bilayer.