Histoid leproma usually occur in pat.ients with lepromatous leproy who have had relapsed after being undcr treatment(usually sulfones) for a long time and who have shown variable improvement. A 56 year old female patient who had been suffering from lepromatous leprosy and had been treated which clapsone relatively regularly for approximately 28 years had a history of several shiny rice grain t.o peanut sized nodules on the face and right flank. Histopathologic examination of a specimen taken from a nodular lesian revealed a well circirmscrihed nodule composed mainly of spindle-shaped cells and epithe:ioi 1 cells on the upper and mid-levmis, and granuloma composed of epithelioid cells, multinucleated wait cells and foamy histiocytes on the lower dermis. In AFB stain, numerous acid-fast bacilli were scatt red dermis and epidermis, especially stratum corneum. This study opplied a polymease chain reaction(PCR) on sections of biopsy tissues and peripheral blood of pat.ient. Positive amplification of a 530 bp fragment was deteated not only in the lesion tissues but also in the per ipher al blood. (Kor J Dermatol 1994; 32(1): 167-171)