Abstract Infiltration of the brachial plexus through the supraclavicular fossa affords satisfactory anesthesia in the upper extremity when other factors preclude the use of general anesthesia. The brachial plexus crosses the first rib in an investment of fascia derived from the sheaths of the scalenus muscles and the prevertebral fascia; its medial aspect lies in relation to the first rib. The derivation and divisions of the plexus are described; these relationships indicate the need for injections at various points to ensure adequate infiltration and satisfactory anesthesia. The technic advocated utilizes the constant relationship of the plexus and the first rib as a means of locating the plexus. By this method it is possible to inject two or more cords of the plexus individually, which provides increased likelihood of successful anesthesia. The necessity of injecting the intercostobrachial nerve for surgery in the arm, and at the tubercle of Chassaignac for surgery about the shoulder must be borne in mind. Observance of a motor twitch in the arm muscles, rather than subjective sensations reported by the patient, is believed to furnish a more reliable indication of contact with the plexus. The results obtained by this method of administration in the writer's hands were good in 87 per cent of cases. The failures are tabulated according to cause; not all the failures were failures of the method itself. The anesthesia obtained permitted major surgery to be carried out with no complaint of pain on the part ot the patient in the successful cases. The average duration of anesthesia was one and three-quarter hours; in cases in which shock was present satisfactory anesthesia not infrequently lasted for three hours.