Many elderly individuals are treated with antibiotics, but knowledge of the pharmacokinetic performance of the compounds in these patients is limited. Advanced age is accompanied by many physiologic alterations that may have secondary effects on absorption, distribution, metabolism, and excretion of drugs. Information on absorption and metabolism in the elderly is scarce and conflicting. Because renal excretion of penicillins and cephalosporins decreases with the physiologic signs of the kidneys, dose reduction is advisable in elderly patients. Monitoring of serum drug levels is recommended for the selection of correct dosages of renally eliminated antibiotics with a narrow therapeutic range--e.g., aminoglycosides and vancomycin. There is a considerable need for additional studies of the influence of age on the kinetics of antimicrobial agents.