Abstract: Apparatus for hypodermically implanting a genitourinary prosthesis comprising an extensible, inflatable tissue expanding containment membrane to be located in the proximal periurethral tissues to add bulk to these tissues and thereby overcome urinary incontinence by means of localized, controlled tissue volume increase. Hypodermic positioning, injecting and inflating instruments are also disclosed for implanting the containment membrane and for percutaneously infusing the membrane with biocompatible fluid or suspended particulate matter. The containment membrane functions as an envelope for retaining the fluid or particulate matter therewith in while controllably and advantageously increasing localized tissue volume and simultaneously preventing the migration of such fluid or particles. Accordingly, an increased passive occlusive pressure may be applied to the patient's urethra to achieve continence.