The in-vitro activity of sparfloxacin was compared with that of pefloxacin, ofloxacin, ciprofloxacin, imipenem, ceftazidime, gentamicin and amikacin against 275 multiresistant nosocomial clinical isolates. They consisted of Pseudomonas aeruginosa (37), Enterobacter cloacae (42), Acinetobacter anitratus (60), Klebsiella pneumoniae (37) and Staphylococcus sp (99). Minimum inhibitory concentrations (MIC90) and geometric mean MICs for sparfloxacin were as follows (mg/l): P. aeruginosa 128-23.7, E. cloacae 1-0.13, A. anitratus 2-0.14, K. pneumoniae 1-0.08, MRSA 16-0.98, MSSA 0.12-0.03, MRSE 0.25-0.12 and MSSE 0.12-0.05. It is concluded that sparfloxacin was the most potent agent against staphylococci and A. anitratus including strains resistant to the other quinolones while ciprofloxacin was the most potent agent against P. aeruginosa, E. cloacae and K. pneumoniae.