Muscarinic agonists alter the metabolism of amyloid precursor protein, leading to an increase in α-secretase cleavage and a decreased production of amyloidogenic peptides; suggesting that these compounds might modify the Alzheimer's disease process. A second therapeutic target in AD is the accumulation of stably phosphorylated tau into neurofibrillary tangles; an early event correlating with cognitive impairment. Glycogen synthase kinase-3 (GSK-3β) phosphorylates tau and is inhibited via protein kinase C (PKC). As certain muscarinic receptors are linked to PKC, we examined the effect of a range of agonists on GSK-3β phosphorylation of tau. In neurons a non-specific muscarinic agonist, carbachol, reduced tau phosphorylation. In non-neuronal cells expressing the m1 receptor a range of m1 agonists reduced transiently-expressed tau phosphorylation and altered its microtubule-binding properties. These findings link the two pathological process of AD - APP metabolism and tau phosphorylation - and suggest that muscarinic and other cholinergic compounds might have disease-modifying properties.