The present invention provides a novel treatment for senile dementia (Alzheimer's Type), comprising administering an anti-complement protein to a patient in need of such treatment in an amount sufficient to inhibit the complement cascade and thereby inhibit the production or enlargement of amyloid plaques in the brain of the patient. The present invention further provides pharmaceutical compositions comprising anti-complement protein, or derivatives thereof, and/or pharmaceutically acceptable salts thereof in a variety of unique pharmaceutical dosage forms.