Thirteen patients suffering from transient acute confusional states (ACS) and 11 patients with probable Alzheimer's disease (AD) who were comparable for age and Mini-Mental State score were investigated with a naming and a comprehension task. The latter included both words that were previously included in the naming task and unfamiliar items. With five patients of each group, the assessment was repeated 1 to 3 days later. The number of misnamings was comparable for both groups. An effect of word frequency upon naming success was found only with the AD group. Unrelated misnamings were significantly more frequent in the ACS group. Closer analysis suggested that part of the unrelated misnamings in the ACS patients were caused by visual misperceptions. Behavioral strategies aiming at the target were more frequently exhibited by Ad patients. Perseverations, especially of the intrusion type, were characteristic for ACS patients and only occasionally found with AD. There was an item consistency over time with naming failure in the AD, but not in the ACS group. Cross-modal performance consistency seemed greater in the ACS than in the AD group.