The case history of a haemodialysis patient with fever and rigors is p
resented. This diagnostic problem turned out to be a hypersensitivity
reaction to azathioprine, with identical complaints recurring after a
rechallenge with azathioprine, findings which resolved on discontinuat
ion of this drug. The more extended indications for use of azathioprin
e warrant attention to the possibility of side-effects like drug fever
.