Vancomycin was administered intravenously to 10 pregnant women for the treatment of methicillin-resistant Staphylococcus aureus infections. Auditory brainstem response testing and renal function studies were performed on the 10 babies in the experimental group and 10 babies in each of two control groups to determine the safety of vancomycin use during pregnancy. Auditory brainstem responses were not normal at birth in six infants from the three different groups studied (N = 30) but were normal at 3 months in five. The sixth infant had conductive hearing loss unrelated to vancomycin use that spontaneously disappeared at 12 months of age. Renal function was normal in all infants. Vancomycin was detected in cord blood in two patients and in breast milk in one. Adequate serum levels were achieved with routine doses in eight mothers tested; no adverse reactions occurred. It appears that vancomycin use during the second and third trimesters of pregnancy does not produce sensorineural hearing loss or nephrotoxicity in the infant.