Seventy-seven patients with Alzheimer's disease were submitted to a double-blind no cross-over study of the effect of a synthetic ACTH4-9 analog (Org 2766) on the EEG. The quantitative EEG power spectrum analysis with 22 Org 2766 and 22 placebo treated patients showed no improvement which could be related to the Org 2766 medication (6 months, 40 mg daily), either comparing the successive EEG sessions or comparing the drug treated group with the placebo treated group. The placebo treated group showed a decrease of power in the beta band after 4 and 6 months and an increase of theta after 6 months, which is regarded as a sign of deterioration of the EEG in advancing disease. These changes did not occur in the Org 2766 treated group. However, a subgroup analysis of 9 Org 2766 treated patients and 9 placebo treated patients without other CNS drugs during the study did not reveal consistent differences between the groups after 4 and 6 months of therapy. We believe that Org 2766 does not have a long-term protecting effect on the EEG.