The time-kill kinetics and post-antibiotic effect (PAE) of moxifloxacin were studied for strains of Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae, Staphylococcus aureus and Escherichia coli. Moxifloxacin had a bactericidal effect against all strains tested, with the least rapid bactericidal effect being against S. pyogenes and the most rapid effect against S. aureus and E. coli. The PAE of moxifloxacin was similar to that of other fluoroquinolones and increased with increasing concentration. No association was found between the bactericidal effect of moxifloxacin and the duration of PAE. Gram-positive and gram-negative organisms were also exposed to concentrations of moxifloxacin, sparfloxacin and amoxycillin that simulated the drug concentrations obtained in human serum after standard oral dosing schedules. Simulation of moxifloxacin concentrations in human serum reduced viable counts more effectively and more rapidly than shown in time-kill experiments; in contrast, sparfloxacin and amoxycillin were less effective than when constant concentrations of these antibacterials were used.