Using simple successive tasks we assessed the influence of Alzheimer's disease on the processing of different odours. Fifteen patients with Alzheimer's disease, 15 old control subjects and 15 young control subjects were tested. The experiment included two sessions. Initially 12 odorants were presented, one odorant every minute. For each odour the subjects were asked to rate intensity, pleasantness, familiarity and edibility using linear rating scales. The odorants were then presented a second time and the subjects were asked to identify them. The results show that the intensity scores were lower in old control subjects and Alzheimer patients than in the young control subjects and that familiarity and identification scores were lower in Alzheimer patients than in old control and young control subjects. When we compared the five olfactory tasks the impairment of performance in Alzheimer patients was relatively higher for identification than familiarity, itself higher than the intensity judgement. No difference was observed between the three groups of subjects for pleasantness and edibility judgements.