Abstract: An electron beam lithography machine comprises a movable support for a substrate, an electron beam column for providing an electron beam to scan the substrate, an optoelectronic monitoring system for monitoring the position of the substrate relative to the column axis, and a rigid mounting body for mounting the support and the column. Laser interferometers of the monitoring system are mounted in mutually fixed relationship on a rigid carriage which is supported relative to the body by rollable members. The rollable members rotatably bear against the walls of grooves in the body and in the carriage in such a manner that the carriage is secured against tilt relative to the body and limited deformation of the body, especially thermally induced expansion and contraction, is accommodated without alteration in the position of the interferometers relative to the axis.