Several investigators have attempted to clarify th well-known phenomenon of anergy in lepromatous leprosy during past two decades, utilizing various methods of immunologic assessrvent, including response to skin test antigens, active skin sensitization with strong allergens, skin homograft survival rate, imrnunopathology of lymphnodes, in vitro blastogenic response by antigens or mitogens of lymphocytes, lymphokine production in vitro and measurement of peripheral T and B cell ratio. Howcver, there is no general agreement as to the cellular irnmunologic status of leprosy patients b tween various investigators. The present study was undertaken to evaluate the ability to mount cutaneous hypersensitivity reactions to various skin test antigens and to investigate active sensitization with DViCB in patients with leprosy. Ten polar lepromatous (LL) and 12 polar tuberculoid (TT) p-tients who have been treated at Department of Dermatology, National Iviedical Center and Seoul Nationa,l University Hospital were the subjects. The subjects have rcceived regular antileprosy chemotherapy with DDS and the average duration of treatment in LL and TT groups was 6. 2 and 4. 7 years, respectively. The control group included 10 healthy physicians and nurs-s. Skin test antigens includ=d lepromin (1 x10' bacilli,ml'), PPD (Parke-Davis 5ppJ /0. 1ml), SK-SD (Lederle, 40 u SK and 10 u SD/0. 1 ml), Candidin (Hollister stier Lab 1: 1000 dilution) and DNCB aceton solution in the concentrations of 1000ug,/ 0. 1ml for sensitization and 100ug/0. 1ml for challenge, respcctively. Skin reactions were read 48 hours after intraderrnal injection of 0. 1 rnl of each antigen anci th.' metho4 of DNCB sensitization was same as described elsewhere. The result showed that in polar lepromatous leprosy patients, the skin reactivity to various antigens were generally decroased, as cornpared to both th healthy control group and polar tuberculoicl patients, especially to lepromin, PPD and I')NCB sensitization (p <0. 05, respectively). We concluded thxt lepromatous leprosy patients were especially unresponsive to mycobacterial antigcns(lepromin and PPD) and to newly administered antigen (DNCB) and tbe possible mechanism was discussed.