Severe cholestatic jaundice occurred in two patients receiving prednisolone and azathioprine, one for chronic progressive hepatitis, the other for Wegener's granulomatosis. Reversible abnormal liver function, involving both elimination and synthesis, was in the foreground clinically. Signs of parenchymal-cell damage were only moderately severe. When azathioprine had been discontinued all previously abnormal values returned to normal within six to eight weeks. Azathioprine is an indirect optional hepatotoxin. If given over long periods there should be regular controls of blood count and liver functions.