Early and delayed complications in the inner or middle ear may follow stapedectomy or stapedotomy and may require revision surgery. Nowadays high resolution middle ear computed tomography (HR-MCT) using a special interpolation technique can demonstrate the smallest structures of the middle ear space, such as the long process of the incus and stapes. Stapes prostheses can also be seen in this way, but to identify the prothesis exactly it is necessary to determine the position of the piston hook in relation to the incus and of the piston shaft to the foot plate and scala vestibuli. Two points were of particular interest to us: HR-MCT identification of various metal and plastic pistons. Clinical significance of HR-MCT in complications following surgery. As the result of our experimental research on cadaver temporal bones, pistons must still be divided into four groups based on their demonstration by HR-MCT: Group I (e.g. Stainless Steel Cup Piston): whole piston visible. Group II (e.g. McGee Stainless Steel Piston): only piston shaft. Group III (Fisch Teflon-Platinum Piston): only hook visible. Group IV (e.g. Fisch Teflon-Wire Piston): piston hardly visible or not at all. In groups I-III it is possible to discover whether the piston is too long or too short, whether it is dislocated or has slipped. Group IV pistons, hooks from group II and the shaft from group III must be changed to allow detection by x-rays. With plastic pistons it might be possible to add an x-ray agent.2+ improvements in manufacture appear to be necessary, dislocation of various prostheses can now be shown.(ABSTRACT TRUNCATED AT 250 WORDS)