To the Editor.— I would appreciate it if you could publish the following correction to my discussion of a patient with alopecia and ichthyosis while on "Zyloprim" brand allopurinol, which appeared in the July 1968 issue of theArchives, p 104. Xanthine oxidase is involved in the metabolism of purines, is probably not essential to cellular metabolism, and is not a cytotoxic agent. Allopurinol is synergistic only with mercaptopurine and azathioprine. The company and the literature suggest that the dose of these drugs be markedly lowered, usually by 75%, that is to 25% of their usual dose, when used together with allopurinol. This combination should be used only by people experienced in the field.