The aim of the present study was to explore a possible interplay between cholinesterase inhibitors (ChEIs) and thyroid function tests (TFTs) in patients with Alzheimer's disease (AD). We reviewed thyroid function tests in 19 patients with AD before and after treatment (Rx) with ChEIs. Immunoradiometric assays were used for measuring serum thyrotropin, free thyroxin (FT4) and free triiodothyronine (FT3). Significant differences were observed among FT3 levels according to the duration of therapy. Subtle variations in thyroid function tests - before and after therapy - could be possibly related to ChEIs-induced altered thyroid function.