The association of fever, nasal congestion and reversible rise in serum creatinine in a patient receiving azathioprine is reported. An identical pattern of symptoms was induced after two rechallenges with azathioprine. The increases in serum creatinine were not associated with renal parenchymal abnormalities. This paper illustrates that in transplanted patients, fever and rises in serum creatinine are not only related to rejection or infection, but may also involve drug hypersensitivity.