This study is investigating the effects of hormone replacement therapy on memory, mental abilities and mood in older adults aged 65-90. During the nine month long study, men will take testosterone for three months and women will take estrogen for three months. At four points during the study (once every three months), participants will complete a test battery and have blood drawn.

Double-blind, placebo-controlled, crossover study investigating the effects of estrogen replacement and testosterone replacement on cognition and mood in older adults. Women who have not had a hysterectomy will be given Prempro (estrogen with progesterone to protect the uterine lining), and hysterectomized women will be given Premarin (estrogen only).

• Cognition Disorders
• Mood Disorders

• Drug: Estrogen
• Drug: Testosterone

• Henderson VW. The epidemiology of estrogen replacement therapy and Alzheimer's disease. Neurology. 1997 May;48(5 Suppl 7):S27-35. Review.
• Janowsky JS, Oviatt SK, Orwoll ES. Testosterone influences spatial cognition in older men. Behav Neurosci. 1994 Apr;108(2):325-32.
• Sherwin BB. Estrogen effects on cognition in menopausal women. Neurology. 1997 May;48(5 Suppl 7):S21-6. Review.

Inclusion Criteria:

• Women and men aged 65-90 who have not received hormone replacement for the last three months.

Exclusion Criteria:

• Previous head injury with loss of consciousness for more than one hour.
• Men with a history of prostate cancer.
• Men on testosterone replacement within the past three months.
• Women with a history of breast or uterine cancer.
• Women on estrogen replacement within the past three months.