There has been considerable interest in cognitive deficits associated with Alzheimer's disease (AD) and relationships between these impairments and specific cortical atrophies. Two previous studies [Neuropsychologia 28 (1990) 1197; Dementia 3 (1992) 350] have found that AD patients exhibit significant impairments in the attentional ID/ED set-shifting tasks of the CANTAB battery which involved attentional shifting abilities. But, at present, no study has examined the neural bases of these abilities in AD patients. In the present study, the relationship between performances on this attentional test and morphometry of the anterior and posterior corpus callosum is examined in AD patients in the mild to moderate stages of the disease (n=30, mean age=74.1+/-4.9 years, mean MMSE score=23.9+/-2.6). A control group is constituted (n=20, mean age=73.15+/-5.5 years) for comparison of cerebral measurements. The stepwise multiple regression analysis indicates that the relative contribution for the total callosal and the anterior CC areas of the simple discrimination subtest is significantly positive whereas for the posterior callosal areas the relative contribution of the more complex subtest is significantly positive. AD patients from the subgroup "low", who failed to do the nine subtests of the attentional set-shifting tasks, exhibit smaller callosal areas than control subjects. There is no significant difference for all callosal measurements between AD patients from the subgroup "high", who completely succeeded the test, and control subjects. Our findings suggest that the anterior corpus callosum would be related to attentional shifting abilities in AD patients. Moreover, these patients with probable AD seem heterogeneous for performances in the attentional test of the CANTAB and for callosal atrophies.