Objective: To examine the efficacy of fluoxetine in the treatment of depression in patients with probable Alzheimer's disease (AD). Methods: This double-blind, parallel-design study included a consecutive series of 41 AD subjects meeting DSM-IV criteria for major or minor depression who were randomized to receive fluoxetine (up to 40 mg/day) or identical-appearing placebo. All patients received biweekly evaluations consisting of the Hamilton Depression Scale (HAM-D) and the Clinical Global Impression as primary efficacy measures, and the Mini-Mental State Exam, Hamilton Rating Scale for Anxiety, and the Functional Independence Measure as secondary efficacy measures. Results: Complete remission of depression was found in 47% of subjects treated with fluoxetine and in 33% of subjects treated with placebo. Both the fluoxetine and the placebo groups showed a significant decline in HAM-D scores over time, but the magnitude of mood improvement was similar for both groups. Fluoxetine was well tolerated, and most side effects were mild. Conclusion: Fluoxetine treatment for depression in AD did not differ significantly from treatment with placebo. Our study also confirms the presence of a placebo effect in the treatment of depression in AD.