The authors report a case of tubulo-interstitial nephritis with acute renal failure due to vancomycin used to treat a patient with enterococcus endocarditis. Rechallenge with vancomycin several days after stopping the drug resulted in the appearance of a maculopapular rash and rapid onset of acute oligo-anuric renal failure. Renal biopsy revealed acute interstitial nephritis. This feature is suggestive of cellular mediated hypersensitivity.