Inhibitory activity of thirty-one ethanol extracts obtained from albedo, flavedo, seed and leaf parts of 17 cultivars of Citrus species from Turkey, the bark and leaves of Olea europaea L. from two locations (Turkey and Cyprus) as well as caffeic acid and hesperidin was tested against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), related to the pathogenesis of Alzheimer's disease, using ELISA microtiter assays at 500 mu g/mL. Metal-chelating capacity of the extracts was also determined. BChE inhibitory effect of the Citrus sp. extracts was from (7.7 +/- 0.7) to (70.3 +/- 1.1) %, whereas they did not show any inhibition against AChE. Cholinesterase inhibitory activity of the leaf and bark ethanol extracts of 0. europaea was very weak ((10.2 +/- 3.1) to (15.0 +/- 2.3) %). The extracts had either no or low metal-chelating capacity at 500 mu g/mL. HPTLC fingerprinting of the extracts, which indicated a similar phytochemical pattern, was also done using the standards of caffeic acid and hesperidin with weak cholinesterase inhibition. Among the screened extracts, the albedo extract of C. limon 'Interdonato', the flavedo extracts of 'Kara Limon' and 'Cyprus' cultivars and the seed extract of C. maxima appear to be promising as natural BChE inhibitors.