Ten patients diagnosed as affected by primary degenerative dementia of the Alzheimer type, with a mild to moderate cognitive and behavioral impairment, were studied in a double blind design when taking for 60 days 5 mg twice a day of L-deprenyl or placebo. Cognitive functions and cerebral blood flow were assessed at the beginning and at the end of treatment by a wide array of memory, attention, and language efficiency measures and by SPECT-99TcHMPAO procedure. Reduced CBF on the parietal lobes was demonstrated in the patients at baseline together with a reduction of memory and cognitive efficiency. At the end of the treatment patients who received L-deprenyl showed an improvement in cognitive efficiency and no changes in CBF, while patients treated with placebo showed a worsening of cognitive efficiency and further reduction of parietal lobe CBF.