Objective:To measure the field-to-microphone transfer function for two sizes of completely-in-the-canal (CIC) devices, at two loudspeaker azimuths.Design:Field-to-microphone transfer functions were measured for both standard- and micro-CIC instruments, at 0° and 45° azimuth, in a sample of 24 adults. This was accomplished with custom instruments, which allowed for a direct connection between the CIC microphone electrical output and the measurement/analysis instrumentation system.Results:For the standard-CIC, the peak in the average field-to-microphone transfer function was 8 dB at 4000 Hz for 0° azimuth and 13.7 dB at 5000 Hz for 45° azimuth.Conclusions:The results demonstrate and define, at two signal azimuths, the acoustic advantage of the CIC microphone placement relative to that reported for alternative hearing aid styles.