Tbe Jotjbnal of Investigative Dermatology

An improved histochemical method for demonstrating tyrosinase activity has been described which utilizes small amounts of dopa to shorten the induction period for the enzymatic oxidation of tyrosine. This method is a rapid, reproducible and specific way to localize tyrosinase in tissue sections. With this method tyrosinase activity was demonstrated in normal and neoplastic melanocytes and in normal and neoplastic mast cells. These observations support previous evidence from this laboratory that some mast cells contain tyrosinase. Supported by TJSPHS Training Grant Ti AM 5220 06 and by an Institutional Grant (General Research Support Fund) Boston City Hospital. Received November 12, 1968; accepted for publication January 29, 1969. Reprint requests to Dr. Okun, Dermatopathology Lab., Boston City Hospital, 818 Harrison Ave., Boston, Mass. 02118. * From The Dermatopathology Laboratory, Boston City Hospital, The Department of Dermatology, Tufts University School of Medicine, and The Department of Pathology, Boston University School of Medicine. t Present address: Department of Dermatology, University of Vienna, Vienna, Austria. 40 TIlE JOURNAL OF INVESTIGATIVE DERMATOLOGY