Effectiveness and tolerability of two piracetam-containing drugs were compared in the frame of an open, multicentre, Phase-IV, prospective study with group and self control carried out in 9 Hungarian centres in 1998. Patients with cognitive decline from Alzheimer's disease and/or cerebrovascular origin have received the drug, in the first 4 weeks in 4800, later 2400 mg daily doses. One hundred four patients finished the study. No relevant difference with statistically significant degree was registered between the two groups. Based on this fact in this study data of the 104 patients were examined together. Authors examined two problems. The first: on which cognitive function is more effective the drug. Five factors of the modified Mini-Mental State Examination were separated and compared. Nearly all of them significantly increased especially the factors of memory, and concentration-psychomotor speed. The second examined field: are there certain subgroups with prognostic value about the effectiveness of piracetam treatment. Neither the duration of the illness, nor etiologic diagnosis, severity of cognitive decline, or former treatment with piracetam did influence significantly the efficacy. In case of depressive symptoms such connection was established: the more pronounced the severity of these symptoms the higher improvement can be expected in cognitive functions. This was also stressed by the logistic regression analysis. Authors described an original evaluation method of the trail-making test, which could widen the application of this popular test in psychopharmacologic studies. Final conclusions: the cognitive enhancer effect of piracetam appeared in a few weeks. This treatment could be effective even in Alzheimer's disease, in case of more pronounced cognitive decline, longer duration of the illness, and in case of former piracetam treatment as well. The degree of cognitive improvement was most pronounced in patients with comorbid depressive symptoms.