This study aimed to explore verbal and spatial memory spans in Alzheimer's (AD) and multi-infarct (MID) demented patients. For this purpose, we administered the forward and backward versions of the Digit Span and of the Corsi test to 18 AD, 18 MID and 26 controls. Results revealed a normal forward verbal span but reduced backward verbal and forward and backward spatial spans in both demented groups. These data are discussed in the light of the Working Memory model. It is argued that the normal verbal forward span is sustained by a normally functioning Articulatory Loop. The deficient processing resources of the Central Executive, on the other side, are responsible for the reduced extension of the other memory spans. The possible anatomical substrate of short-term memory impairment in dementia, as well as alternative interpretations of memory span performance in demented patients are discussed.