Abstract: An alignment apparatus for aligning x-ray images with a predetermined set of axes comprises means defining the axes in the form of a support arrangement which supports, at predetermined positions in space, located in at least two predetermined planes, a plurality of elements which are opaque to ex-radiation. An apparatus is also described for aligning an end effector comprising two spaced guide frames each having two parallel guide members with a carriage for movement along each of the guide members, the carriages being inter-connected by cross members, further carriages being mounted on the cross members, the further carriages supporting the end effector for guide means.