We evaluated the pharmacokinetics and adequacy of gentamicin or tobramycin after administration of a loading dose of 3 mg/kg body weight in 14 critically ill patients with presumed sepsis. Therapeutic blood levels after loading dose were obtained in 13 of the 14 patients. Measured volume of distribution, serum half-life, and elimination rate constant were significantly different from values calculated by using standard formulae. All the patients tolerated the dose well without significant deterioration in renal function. Based on the present study, we conclude that administration of 3 mg/kg body weight loading dose of gentamicin or tobramycin in critically ill patients with sepsis would result in earlier therapeutic drug levels.