The present invention relates to a combination of a first agent including either a 5-HT.sub.4 receptor agonist or antagonist or a 5-HT.sub.3 receptor antagonist and a co-agent and pharmaceutical compositions and formulations containing the combination. The present invention also relates to a method of treating a gastrointestinal and abdominal viscera disorder by administering the pharmaceutical compositions to a patient. The pharmaceutical compositions may also be employed as laxatives, to prepare a patient for colonoscopy and to regulate and stabilize enterochromaffin cell secretory, pain and motility mechanisms, afferent fiber activity and GI and lower abdominal smooth muscle cells. The dosage is preferably oral and administration is preferably once or twice a day. The preferred first agent is tegaserod.