A phantom is described which has been developed for investigating factors depending on the scanner itself and on the scanned object which potentially influence the kind and the extent of motion artefacts on the CT-image. Additionally, the phantom may be applied to qualify assurance measurements in computer tomography. A cylindrical insert mounted on a motor driven axis is fitted centrally in a cylindrical block machined from lucite. Two interchangeable inserts are available, one containing test objects made of various materials, and another one containing small vessels which can be filled with test solutions. The insert positioned in the phantom can rotate either continuously or with the direction of motion being altered periodically. Speed, frequency and arc can be varied within wide limits. Examples demonstrating the static and the dynamic mode of the phantom are shown. By means of the dynamic phantom it is quite easy to directly determine the scan-time of a Computer tomograph.