One hundred and nine elderly patients suffering from mild to moderate cognitive impairment fulfilling NINCDS-ADRDA criteria for probable dementia of the Alzheimer type were treated for 6 months with a new nootropic drug, aniracetam (Ro 13-5057) in a double-blind randomized study versus placebo. The two treatment groups were comparable at baseline for demographic and behaviourial parameters and symptomatology. Patients underwent clinical, behaviourial and psychometric evaluation every other month. The aniracetam group differed significantly from the placebo group by the end of the study and also showed a statistically significant improvement versus baseline in the psychobehavioural parameters, while in the placebo group a steady deterioration was observed. Tolerability to aniracetam was excellent.