The serum half-life of kanamycin sulfate following an intramuscularly administered dose was compared to the serum creatinine concentration in ten adult patients with different degrees of renal failure. Because a linear correlation was found, the kanamycin half-life (in hours) could be estimated by multiplying the serum creatinine concentration (mg/100 ml) by three. As the apparent distribution volume for kanamycin is similar to the extracellular volume and averages 19% of body weight, an injection of 7 mg/kg of body weight will result in therapeutic drug levels. Kinetic analysis predicts that repetition of this loading dose every third half-life will result in therapeutic, nontoxic serum levels in patients with renal failure.