It is the ability of a drug to reach and maintain effective concentrations at the infection site that determines its efficacy. This article reviews the pharmacokinetics and pharmacodynamics of antimicrobials used in the treatment of meningitis. A better understanding of the interrelationship between pharmacokinetics-the time course of antimicrobial concentrations in serum and at the infection site-and pharmacodynamics-the relationships between antimicrobial concentration and antimicrobial effect-should facilitate the establishment of optimal dosage regimens for this life-threatening bacterial infection.