This study investigates three principal aspects of semantic memory processing in Alzheimer's disease: word finding, knowledge of the specific and generic attributes of concepts. Semantic memory is assessed by a range of verbal and visual tasks differentiated according to their level of complexity. Our hypothesis is that the processing of these types of information is modulated by the degree of effortful processing required by the tasks. The AD patients show more important difficulties on the tasks of high level of complexity. Nevertheless, although their performances improve when the level of complexity decreases, they significantly remain lower than those of the normal older subjects. These results are discussed with regard to the models of semantic memory, with particular reference to the debate in terms of a deficit of access or storage of this system in Alzheimer disease.