The HEARing Cooperative Research Centre, Australia. firstname.lastname@example.org. au Summary The accurate reproduction of acoustic real-world environments is becoming of increasing importance in hearing device research and development. It is thereby often required to accurately predict the sound pressure at the microphones of a hearing device in a simulated or recorded acoustic environment. For that reason, an extensive set of head-related transfer functions (HRTFs) was measured in free-field with a pair of behind-the-ear (BTE) hearing aids placed on a Head and Torso Simulator (HATS). Transfer functions to the in-ear HATS microphones were also measured. A spherical head model was applied to extend the useable frequency range towards low frequencies. Special care was given to preserve the phase properties of the measurements so that the HRTFs could be widely used in phase-sensitive technical applications, including the evaluation of spatial signal processing algorithms (i.e. directional microphones, beamformers) in hearing devices and the evaluation of sound field resynthesis methods. The extended HRTF set can also be used for research in psychoacoustics. It is available for download at: http://www.nal.gov.au/ download/HATS-BTE-hrirDatabase.zip.