Twenty-one patients with refractory idiopathic constipation underwent studies of segmental colonic transit of radiopaque markers and anorectal manometry to determine the utility of these tests in planning therapy and in predicting subsequent clinical outcome. Colonic transit studies defined three groups: normal transit (n = 6), colonic inertia (n = 8), and distal slowing (n = 7). Normal transit was universally associated with evidence of psychosocial disturbances. During follow-ups ranging from 23.2 to 26.7 months, six of eight patients with colonic inertia failed to improve compared with only one of seven with distal slowing. Anorectal manometry was useful in excluding abnormalities of anorectal function. Segmental colonic transit of radiopaque markers is a simple and useful test in the evaluation of refractory idiopathic constipation and appears to have both prognostic and therapeutic utility in selected cases.