Cerebrospinal fluid (CSF) diffusion of kanamycin was studied in 35 newborn infants. Five infants had bacterial meningitis and two had viral meningitis. One-half of the infants received an intramuscular injection of 7.5 mg of kanamycin per kg, whereas the other half received 12.5 mg/kg. Serum and CSF specimens were obtained 3 to 6 hr and 11 to 12 hr after injection. No significant difference was observed between serum levels of kanamycin after the 7.5 and 12.5 mg/kg doses at either sampling time. However, at 3 to 6 hr, in those infants without meningitis, there was a significantly higher concentration of kanamycin in the CSF after the larger 12.5 mg/kg dose. CSF levels of kanamycin did not rise to the desirable therapeutic range with either dose. We were unable to draw a definite conclusion regarding the CSF diffusion of kanamycin in bacterial meningitis, but our data suggest that complete confidence in intramuscular kanamycin in the treatment of gram-negative neonatal meningitis may not be justified, even in those cases with a brisk inflammatory response.