We have applied a new method of assessment of bactericidal activity in vivo. Calculation of area under the bactericidal activity curve (AUBC) provides a value which involves both the in-vitro bactericidal activity of the drug and its pharmacokinetics. With this method, the activity of combinations of antimicrobials can be assessed in vivo by comparing the AUBC obtained from the combination vs the sum of AUBC from each drug alone. This method may allow a more rational selection of dosage regimens and drug combinations for the treatment of infections.