Levofloxacin, an optically active isomer of ofloxacin, is a fluorinated quinolone with a broad spectrum of antibacterial activity. Fluoroquinolones have been used for the treatment of bacterial infections for many years. Although they were considered as relatively safe drugs, various adverse effects have recently been reported along with increase in the usage of new-generation fluoroquinolones. In the present study, some of the central nervous system (CNS)-related side effects of levofloxacin were clarified in animals. Our results suggested that: levofloxacin (10-20-40 mg/kg ip) had no depression-like effect in the forced swimming test (FST) in rats; exerted anxiety-like effect in the elevated plus maze test in rats did not alter the locomotor activity in rats; had no apparent effect on sleep latency but shortened the sleeping time on pentobarbital sleeping time in mice; and showed analgesic activity in acetic acid writhing and hot plate test in mice. (C) 2001 Elsevier Science Inc. All rights reserved.