The major compounds isolated from the methanolic extract of the aerial parts of Urtica dioica L. were determined as quercetin-3-O-rutinoside (1), kaempherol-3-O-rutinoside (2) and isorhamnetin-3-0-glucoside (3) by chromatographic, chemical (acidic hydrolysis) and spectral (UV, IR, H-1-NMR, C-13-NMR) methods. Their immunomodulatory activities were studied in vitro by chemotaxis (Boyden Migration Chamber) and intracellular killing activity (NBT reduction) tests. Compounds 1, 2, 3 and the total flavonoid fraction were determined to have significant chemotactic effects in 4, 8, 16 mug doses. According to the results of the NBT reduction test, all flavonoid glycosides showed high intracellular killing activity. The results of both assays confirmed the immunostimulatory activity of the flavonoid fraction and the isolated flavonoid glycosides on neutrophils suggesting that they could possibly be useful for treating patients suffering from neutrophil function deficiency and chronic granulomatous diseases. Copyright (C) 2003 John Wiley Sons, Ltd.