To the Editor: Could Lin et al. (Aug. 3 issue)1 give their recommendations on how to treat transplant recipients with gouty arthritis? The care of these patients is complicated by the existence of a potentially serious drug interaction between allopurinol and azathioprine. Allopurinol is a xanthine oxidase inhibitor and an important part of the armamentarium for the treatment of gout. Azathioprine is an immunosuppressive agent used primarily with cyclosporine and prednisone for the prevention of organ rejection in transplant recipients. The pathway responsible for the metabolism of azathioprine is xanthine oxidase. The inhibition of this pathway may therefore result in.