Despite growing interest in the formation of domains or `rafts' in cell and model membranes, there have been relatively few attempts to characterize such systems
viascattering techniques. Previously [Pencer et al.(2006). J. Appl. Cryst. 39, 293–303], it was demonstrated that the Porod invariant, Q, could be used to detect lateral segregation. Here, the general theory for scattering from laterally heterogeneous vesicles is outlined and form factors are derived for vesicles containing either single circular or annular domains. These form factors are then applied to the analysis of neutron scattering data from heterogeneous vesicles. Potential advantages and limitations of this technique are also discussed.