Edema of the lower extremities is a difficult clinical problem. It can be due to stasis, obstruction of the lymphatic channels, increased production of lymph beyond the drainage capacity of the lymphatic vessels. It is often difficult to differentiate between these varieties. Lymphoscintigraphy was performed on 164 patients complaining of swelling of the lower extremities and on 5 volunteers. All patients were injected with 1 mCi of Tc-99m human serum albumin (HSA) intradermally in the medial web of the dorsum of each foot. Data were acquired dynamically for both inguinal regions for 45 minutes, and static images of the legs, thighs, and pelvis were taken at 90 minutes. Time activity curves were generated for the equal regions of inguinal nodes on both inguinal sides. The following patterns were recognized: normal (5 volunteers and 57 patients), enhanced (17 patients), stasis with mild obstruction (70 patients), and marked stasis with obstruction (20 patients).