BiCuOSe, which crystallizes in the same structure as LaFeAsO, is a new promising thermoelectric material. During previous experiments on these samples, we have observed an electrical resistivity anomaly. From our XRD study, it seems that this anomaly cannot be ascribed to structural changes, and magnetic susceptibility measurements have not been conclusive. However it is very similar to other results obtained for LaFeOAs. For this latter material, the anomaly can be attributed to the emergency of a spin-density-wave coupled to a structural transition. As preliminary experiments have shown additional peaks below the anomaly temperature in neutron diffraction patterns, we propose to use neutron powder diffraction to study the evolution of this anomaly between doped and undoped compounds in order to understand its origin.