In this work, we present an experimental analysis of a Dialogue System for the automatization of simple telephone services. A first evaluation of a preliminary version of the system was done based on the Speech Recognizer error rate and on the identification of two groups of users, that we refer to as group A and B. From this evaluation we conclude the necessity to design a robust and exible system suitable to have different dialogue control strategies depending on the characteristics of the user and the performance of the speech recognition module. A system adaptation procedure combining a normalized average number of utterances per task, the amount ofinformation in some particular utterances, and an estimate of the recognition error rate. Our adaptation procedure defines two different control management strategies for a exible mixed-initiative strategy: _xed for high recognition errors and Group B users, and mixed for low error rates and A users. Experimental results following the PARADISE framework showed an important improvement.