Investigations into the development of cognitive impairment in 30 hospitalized depressive patients have suggested that such disturbances encompass two dichotomous entities: a core entity of long-persisting, therapy-resistant impairment and an entity of reversible impairment with a prompt onset of improvement. The course of improvement turned out to evolve largely independently with respect to psychopathology: about one half of patients displayed severe cognitive dysfunctions which remained virtually unchanged until hospital discharge, while 80% significantly improved within the first 12 days with respect to their depressive symptoms, and 53.3% displayed a clear response to treatment at the time of hospital discharge. In particular, a considerable number of patients with a significant reduction of depressive symptomatology at hospital discharge still suffered from severe cognitive dysfunctions. Neither antidepressant or antipsychotic medication nor acute side effects due to medication explained the development of cognitive impairment. Accordingly, cognitive impairment seems to represent an essentially independent syndrome complex comparable to 'deficits' or 'negative symptoms' in schizophrenia. On the other hand, single case correlation analysis revealed a somewhat closer relationship of cognitive impairment with speech behavior and voice sound characteristics. Two thirds of patients displayed significant correlations between cognitive performance scores and second-order constructs like speech flow, dynamics or intonation. However, the respective subgroups defined by significant correlations with single speech parameters were relatively small (< or = 35% of cases), thus indicating that there exist large interindividual differences as to how cognitive impairment affects the patients' speech.