The technic of lymphangiography, or the injection of radiopaque material into lymphatics for their demonstration, was described in 1952 by Kinmonth (1). The procedure has since been used to study obstructive edema (2, 3), inflammatory disease, and extension of lymph node metastasis; to evaluate the completeness of pelvic lymphadenectomy (4); and to aid in the diagnosis (5, 6) or staging of lymphomas (7). The lymphangiographic changes of idiopathic retroperitoneal fibrosis have not previously been reported in the radiologic literature. Three cases studied by lymphangiography at the Massachusetts General Hospital will be presented here. The procedure may be of value in establishing the diagnosis of this condition earlier than is now possible with plain roentgenograms of the abdomen, or intravenous or retrograde pyelography. Idiopathic retroperitoneal fibrosis causing ureteral obstruction is a relatively uncommon clinical entity. Approximately 100 cases have been reported in the literature since the original description by Ormond in 1948 (8). The etiology remains obscure, as the proposed theories do not explain all cases. Because there are no specific symptoms, irreparable renal damage may result before a diagnosis is made (9–11). Although retroperitoneal fibrosis may be suggested by loss of the normal fat lines outlining the various retroperitoneal structures (psoas and lumbosacral muscles) on plain radiographs of the abdomen (12), the definitive diagnosis is made at surgery. Currently, intravenous pyelography is the primary preoperative procedure for demonstrating the abnormality, which is reflected in the urinary system by delay of excretion of contrast material, dilatation of the minor and major calyces and/or the renal pelvis, or complete obstruction of one or both ureters (13). The ureters may taper gradually to the point of obstruction and be deviated medially. Retrograde pyelography may also be necessary to demonstrate many of these findings. Methods and Materials The skeletal lymphatics are visualized by injecting the first two web spaces of the feet intradermally and subcutaneously with a mixture of 0.5 c.c. of 11 per cent patent blue violet dye and 0.5 c.c. of 2 per cent lidocaine hydrochloride after a surgical preparation of the field. The dye rapidly enters the lymphatics. The skin on the dorsum of each foot is anesthetized with 2 per cent lidocaine hydrochloride, and a dye-filled lymph vessel is exposed by a surgical cutdown and punctured with a 27-gauge needle tip attached to a 20-gauge polyethylene tube. Approximately 8 c.c. of Ethiodol or Chlorophyll-Ethiodol (an ester of poppyseed oil containing 37 per cent iodine) is injected into the exposed lymph vessel of each extremity with a constant infusion pump, at the rate of 0.136 ml./min. Immediately after the injection is initiated, roentgenograms are made to exclude extravasation.