Defecography, pelvic floor electromyography, and segmental colonic transit times were performed in 74 patients with functional constipation. Signs of functional outlet obstruction occurred in 74 percent. Transit times were normal in 33 percent. Measurement of colonic transit time in patients with disordered evacuation studies is useless from a clinical point of view, because abnormal segmental transit time is the result of outlet obstruction in most cases and will return to normal after adequate treatment. Only when evacuation studies are normal, or have become normal after treatment and constipation persists, are segmental transit studies indicated because they may demonstrate primary slow transit constipation. Primary slow transit constipation probably is caused by impaired motility of the whole gastrointestinal tract. As small-bowel transit time increases, defecation frequency decreases, laxatives are taken again, and abdominal pain persists. Surgery should be performed with restraint.