A macroscopic one-axis movement with picometer resolution was made possible by a feedback loop driving a piezoelectric element locking an elastic guide to a reference value, or to a reference path. The guide displacement has been measured by a high-resolution optical interferometer. Not only were prompt and accurate positionings obtained, but disturbances due to seismic noise were also compensated for. In contrast to conventional positioning, driver linearity and stability, antivibration support, and maximum displacement are not subjected to strict conditions. The performances of an x-ray interferometer were greatly improved by this feedback: the positioning with 1-pm resolution over 30-Hz bandwidth and 0.1-mm maximum displacement was made