Conclusions. This prosthesis has the advantage of rapid adjustment at the time of insertion in order to achieve optimal tension and, as a result, optimal sound transmission. Objective. To test the acoustic performance of a new, adjustable incus replacement prosthesis in a human temporal bone model. Material and methods. Experiments were performed in seven human temporal bones, before and after removal of the incus and insertion of the prosthesis. The input comprised 406 pure tones ranging in frequency between 0.1 and 10 kHz at an intensity of 80 dB SPL at the tympanic membrane. The output measurement was stapes footplate displacement, determined by means of a laser Doppler vibrometer. Three lengths of the prosthesis were investigated: optimal, optimal +0.2 mm and optimal +0.4 mm. Results. The optimal-length prosthesis produced similar results to those of an intact middle ear. The slightly longer prostheses decreased middle ear sound transmission at all test frequencies, except those near 1.5 kHz.