Myeloperoxidase staining methods for classification of leukemias have traditionally employed benzidine dihydrochloride as the chromogen. Recent Occupational Safety and Health Administration regulations have classified benzidine as a carcinogen, which severely restricts its use in the clinical laboratory. Twenty-two specimens from normal control subjects and leukemia patients, previously classified by FAB criteria, were stained with benzidine and two alternate chromogens, diaminobenzidine and Hanker-Yates reagent (p-phenylenediamine and pyrocatechol). In a random, blind fashion, three experienced observers scored the stains from each case according to quality of smear, degree of peroxidase positivity, tinctorial distinction between nucleus and cytoplasm, and overall acceptability of the stain. All three observers rated the substitute chromogens as adequate for routine myeloperoxidase cytochemical staining. It is concluded that either of the methods studied would have clinical utility and can substitute for benzidine as a myeloperoxidase chromogen.