The pharmacokinetics of kanamycin and gentamicin were studied after intramuscular (IM) and intravenous (IV) (constant infusion over 20 minutes)administration in newborn infants. The serum concentrations, halflives,area-under-the-curve values, and volumes of distribution were similar for each drug after both routes of administration. Based on these pharmacological similarities, it is likely that these aminoglycosides can be given safely and effectively as constant IV infusions to neonates in whom IM injections are not feasible.