The purpose of this paper is to illustrate, by means of high-magnification photomicrographs, the characteristic type of cell found in lesions of a case of Kaposi's sarcoma (idiopathic multiple hemorrhagic sarcoma) and thus to attempt to throw some light on the controversial subject of the cell origin of this disease. We also wish to report the effect of cortisone and corticotropin (ACTH) on the clinical course in this case of Kaposi's sarcoma. REPORT OF A CASE J. I., a 71-year-old Italian man, was admitted to the Jewish Hospital of Brooklyn on Nov. 24, 1951, with complaints of swelling, itching, and inflammation of the legs of several years' duration. Twelve years previously, a small, itchy, purple-red papule appeared on the dorsum of the left ankle. This remained unchanged until four years later, when a number of small similar lesions appeared in the same area, with simultaneous increase in size of the