Existing cholinesterase (ChE) inhibitor therapies for Alzheimer's disease (AD), while effective in improving cognitive, behavioral and functional impairments, do not alter disease progression. Novel drug design studies have focused on the classical ChE inhibitor, (-)-physostigmine, producing alterations in chemical composition and three-dimensional structure, which may offer an improved therapeutic index. The phenylcarbamate derivative, (-)-phenserine, is a selective, non-competitive inhibitor of acetylcholinesterase (AChE). In vivo, (-)-phenserine produces rapid, potent, and long-lasting AChE inhibition. As a possible result of its preferential brain selectivity, (-)-phenserine is significantly less toxic than (-)-physostigmine. In studies using the Stone maze paradigm, (-)-phenserine has been shown to improve cognitive performance in both young learning-impaired and elderly rats. In addition to reducing inactivation of acetylcholine in the brain, (-)-phenserine appears to have a second mode of action. Reduced secretion of beta-amyloid (Abeta) has been observed in cell lines exposed to (-)-phenserine, occurring through translational regulation of beta-amyloid precursor protein (beta-APP) mRNA via a non-cholinergic mechanism. These in vitro findings appear to translate in vivo into animal models and humans. In a small study of patients with AD, (-)-phenserine treatment tended to reduce beta-APP and Abeta levels in plasma samples. Clinical studies also reveal that (-)-phenserine (5-10 mg b.i.d.) had a favorable safety and pharmacological profile, produced significant improvements in cognitive function and was well tolerated in patients with AD treated for 12 weeks. Further randomized, double-blind, placebo-controlled Phase III studies assessing the efficacy, safety/tolerability and potential disease-modifying effects of (-)-phenserine in patients with AD are currently ongoing.