Forty clinical isolates of Bacillus anthracis were studied. The MIC90 values of penicillin G, doxycycline, ciprofloxacin, gatifloxacin, and levofloxacin were 0.016, 0.03, 0.06, 0.06 and 0.12 mg/l, respectively. Susceptibilities suggest that the quinolones may also be considered as an alternative therapy for anthrax. (C) 2003 Elsevier Science B.V. and the International Society of Chemotherapy. All rights reserved.