An interactive voice response (IVR) system comprises a memory storing recorded segments of speech by individuals, and a processor configured to enrol individuals. The enrolment process may comprise retrieving one or more of said recorded segments of speech by an individual from said memory and using the retrieved segments to create a voice print for the individual. The suitability of the voice print for authenticating the individual in an IVR system is then tested. This may be done using segments of speech of a predetermined maximum duration such as three seconds or some other amount commensurate with the typical duration of a voice response in an IVR system. An individual may be enrolled as suitable for IVR authentication if the voice print passed the suitability test. Individuals may be authenticated using a voice print only if the voice print has passed the suitability test.