This study presents normal values of bowel habits, colonic transit times of radioopaque markers, and anorectal pressure obtained from 114 normal subjects. Their stool frequency ranged from 3 to 11 per 7 days, whereas their diet contained an average of 14.4 g of crude fibers. Radioopaque markers progressed regularly along the large bowel and a range of transit times was established for its different segments. Manometric studies included measurements of anal pressure at rest, amplitude and duration of the rectoanal inhibitory reflex, anal inflation reflex, and amplitude of rectal contraction in response to rectal distension. Normal ranges were established. Amplitude, duration and magnitude (as measured by planimetry) of anal relaxation elicited by rectal distensions were related to rectal distending volume (P less than 0.001). The incidence of spontaneous variations of anal pressure at rest and of overshoot of pressure after the inhibitory reflex was also established. These data obtained on normal subjects may be compared to those obtained in patients with constipation in order to define the symptoms and to understand pathophysiological mechanisms. This has been done in a companion study.