This paper investigates the behavior patterns (both vocal and gestural) of Alzheimer patients and multihandicapped persons communicating with peers and therapists in an interaction situation. Communicative items were analyzed automatically and sorted into patterns. The results showed that despite their reported 'linguistic' disabilities, the patients not only played their role in the interaction, but were also able to lead the conversation and take initiatives. In spite of their vulnerability, both types of patients, particularly those with Alzheimer's disease, exhibited the ability to integrate new information and to get involved in the dialogue.