Abstract. This paper presents research into using otoacoustic emissions (OAE) as a biometric. OAE are a group of sounds emitted by the cochlea of the ear. The main types are spontaneous OAE which are continuously emitted and the transient and distortion product types which are emitted after stimulation. In this paper the characteristics of OAE are examined to determine the most suitable emission for use as a physiological biometric. The uniqueness of transient OAE are characterised from a data set of 2009 random individuals by a closed rank test. Details of a low-cost portable prototype OAE acquisition system developed at Southampton University are discussed.