An auditory localisation task involving 360 degrees azimuth was performed by three subjects in a large anechoic chamber. A single sound source of a rotating form was employed. Responses were measured to the nearest 10 degrees of azimuth. Under a control condition of 'no helmet' localisation was within measurement errors for all degrees of azimuth. Under conditions of a DH-178 helmet in passive mode, the response field narrowed considerably, and with DH-178 active a further narrowing of the response field occurred. A DH-140 helmet in active mode showed the most degradation of response field. With the helmets in the active mode all sounds were heard as emanating from inside the head.