To confirm the tional diagnosis, rectal biopsy is performed either prepar surgically to obtain a full-thickness biopsy specimen or by the bo suction biopsy for histologic evidence of the absence of gan- flora v glion cells. A noninvasive procedure that may be used is ano using rectal manometry, in which a catheter with a balloon attached compl is inserted into the rectum. The test records the reflex pressure freque response of the internal anal sphincter to distention the of sho of balloon. A normal response is relaxation of the internal sphinc as pla ter followed by a contraction of the external In HD toms the external sphincter contracts normally but the internal diste sphincter fails to relax.