During the past few years an occasional case has been observed of an inflammatory condition selectively involving the temporal arteries which differs clinically and pathologically from the conditions classed under the headings of thromboangiitis obliterans, periarteritis nodosa and rheumatic arteritis. Biopsy shows that the attack of the invasive agent is centered on the medial coat, producing moderate necrosis with hemorrhage at times, and that destroyed areas are replaced with granulation tissue in which numerous giant cells are invariably present. All coats may be involved, which results in intimal thickening and round cell infiltration of the adventitia, and the process may extend to tissues around the arteries. The lumen of the vessel may be closed by thrombosis. Formation of small aneurysmal sacs arising in the media is not observed in this disease as it is in periarteritis nodosa. The cause of this clinical syndrome is unknown, and for want of better