To evaluate the effect of 6 or 12 infusions of differenct dosages of IVIG 10% at regular study visit intervals on the reduction of amyloid beta peptide antibody in the CSF and the increase in the blood plasma in patients with mild to moderate Alzheimer's disease.

To evaluate the effect of 12 infusions of 0.1 g/kg, 0.25 g/kg or 0.4 g/kg IGIV 10% at a 2-week +/- 3 days interval or 6 infusions of 0.2 g/kg, 0.5 g/kg or 0.8 g/kg body weight IGIV 10% at a 4-week +/- 5 days interval on the reduction of +/- in the CSF and the increase in the blood plasma in mild to moderate AD patients.

• Active Comparator: 1
  .1 g/kg IVIG @ 2 week infusion intervals
  Intervention: Biological: IVIG
• Active Comparator: 2
  .25 g/kg IVIG @ 2 week infusion intervals
  Intervention: Biological: IVIG
• Active Comparator: 3
  .4 g/kg IVIG @ 2 week intervals
  Intervention: Biological: IVIG
• Active Comparator: 4
  .2 g/kg of IVIG infusions at 4 week intervals
  Intervention: Biological: IVIG
• Active Comparator: 5
  .5 g/kg of IVIG infusions at 4 week intervals
  Intervention: Biological: IVIG
• Active Comparator: 6
  .8 g/kg of IVIG infusions at 4 week intervals
  Intervention: Biological: IVIG
• Placebo Comparator: 7
  Placebo infusion given at 4 week intervals
  Intervention: Biological: IVIG
• Placebo Comparator: 8
  Placebo infusions given at 2 week intervals
  Intervention: Biological: IVIG

Inclusion Criteria:

• Probable AD according to NINCDS-ADRDA criteria
• Age: 50 to 85
• MMSE: 16 to 26
• Sufficient language skills for testing
• Sufficient vision and hearing for testing
• Modified Hachinski-Rosen Score < 5
• MRI of the head consistent with the diagnosis of AD
• Caregiver with contact at least 4 days per week for greater than 1 hour available
• Outpatient status or assisted living
• Post-menopause (women) as evidenced by lack of menstruation for at least 12 consecutive months or by having bilateral oophorectomy
• Stable doses of approved AD medication(s) for at least 3 months prior to screening (e.g. AChE inhibitors, memantine)
• Normal vital signs or clinically insignificant, if outside normal limits
• Laboratory findings within normal limits or clinically insignificant, if outside normal limits
• Normal ECG or clinically not significant, if outside normal limits

Exclusion Criteria:

• Other causes of dementia (e.g. vascular dementia, Lewy-body dementia, fronto-temporal dementia, Creutzfeld-Jacob disease, Huntington's disease, Parkinson's disease)
• History of or present significant other diseases of the central nervous system (e.g. brain tumor, normal pressure hydrocephalus, Parkinson's Disease, stroke, severe brain trauma, brain surgery, epilepsy, encephalitis)
• Geriatric depression scale of > 7 (short form with scale from 0 to 15)
• Present significant psychiatric disorder (e.g. major depression)
• History of psychosis or hallucinations
• Mental retardation
• Unstable medical disease in the opinion of the investigator
• Insulin dependent diabetes mellitus
• Acute infectious disease
• Vitamin B12 deficiency, though on stable replacement therapy for at least 3 months is acceptable
• Unstable thyroid dysfunction
• Uncontrolled hypertension
• Severe liver or kidney disease
• Major surgery within three months prior to screening
• Prohibited medications: antiepileptic drugs, antipsychotics (but allowed for treatment of acute episodes), antiparkinson agents, anticholinergic drugs, selegiline, MAOI, tricyclics, immuno¬suppressive medications, anti-histamines (unless on a stable dose for at least 3 months or used for treatment of acute episodes), benzo¬diazepines (but allowed for treatment of acute episodes), and Lithium
• Antidepressants are permitted, if on stable dose for at least 3 months and without significant anticholinergic side-effects
• Peripheral venous conditions, which impair establishing regular venous access for infusions
• Medical conditions, which interfere with protein catabolism (e.g. nephrotic syndrome)
• Known blood hyperviscosity, or other hypercoagulable states
• Deep vein thrombosis within preceding 4 years
• Symptomatic stroke
• Transient ischemic attack (TIA) within preceding 2 years
• Participation in other drug trial within the previous 3 months before screening
• Participation in immunological treatment studies of AD other than with IGIV within the previous 6 months before screening.
• IGIV use in the previous six months
• Live viral vaccination within the last month before study entry.
• Not eligible for lumbar puncture (anticoagulant therapy, coagulation disorders, severe spinal alterations)
• Patients with a past or present history of drug abuse or alcohol abuse within the preceding 5 years