Experiments were performed in 22 fresh human temporal bones to compare the relative acoustic function of three stapes footplate sites for an incus stapes superstructure replacement prosthesis (I-SRP). The three sites evaluated were the anterior, centre and posterior footplates. A new round window (RW) measurement method was used to make the comparisons. A small glass microsphere was placed in the centre of the RW as a target. A Polytec laser Doppler vibrometer was used to measure round window displacement in response to 50 pure tones between 200 and 10,000 Hz presented at 80 dB SPL at the tympanic membrane (TM). After a baseline measurement of RW displacement in the intact temporal bone, the incus was removed and a cement I-SRP (CIRP) formed between the mid-malleus handle and each of the three test footplate sites, in random order. RW displacement was again measured after placement of the CIRP at each of three sites. We found the centre site to be 3.0-7.0 dB better than the anterior site above 2,000 Hz. There were no differences between the anterior and centre sites below 2,000 Hz. The posterior site was the worst at all frequencies.