Intermodulation distortion arises when a non-linearity causes two or more signals to interact. We investigated this distortion mechanism by measurement and listening tests using three models of high-quality loudspeaker. Our aim was to discover whether intermodulation distortion of ultrasonic (i.e., above 20 kHz) signal elements could lead to their detectability and confound listening tests or otherwise modify the listening experience. The paper concludes that while such distortion can be found and must be accounted for in some psychoacoustic threshold experiments, it is not pertinent to playback of current high-resolution recordings.