SUMMARY Manometric studies of the sigmoid colon were performed on 17 healthy volunteers and on 49 constipated patients, after a long period of fasting (18-20 hours). Motility was recorded using perfused catheters at basal level during 45 minutes, then 30 minutes after a 0 5 mg intravenous injection of neostigmine, and, finally, 30 minutes during and after a meal. Motor activity was assessed by a motility index (per cent of activity x mean amplitude of waves). In both normal and constipated patients, the basal motility index was very low (respectively 82 +16 and 110 + 113). This low level of activity was due to the long fasting period imposed on all the subjects. After neostigmine the motility index increased in both controls (347±256) and constipated patients (311±323); this test, however was found to be unreliable. The meal increased the motility index to significantly higher values than after neostigmine in controls (538±215). In constipated patients the mean meal motility index was comparable with that of controls (577 ±549) with a large distribution of individual values. Using the mean meal motility index ±2 SD of the control group as a term of comparison, the patients were segregated into three groups: 'hypomotor' patients (eight cases), 'normomotor' patients (33 cases), and 'hypermotor' patients (eight cases). From the evidence of this series of clinically well-defined constipated patients, it was concluded that only the meal test is able to segregate three significant patterns of sigmoid activity and that a large number (68%) of constipated patients exhibit normal sigmoid motor activity.Abnormal motor activity of the sigmoid colon has been described in various disorders, including the irritable colon syndrome, diverticulosis of the colon, diarrhoeal states, and constipation (Connel, 1962;Wangel and Deller, 1965;Kirwan and Smith, 1977). It has been shown that, in constipation, the colonic motor disorder consists mainly in over-segmentation: regardless of the underlying disorder, an over-active sigmoid colon inhibits the transit of stools (Chowdury et al., 1976). However, in previous studies of colonic motility (Meunier et al., 1978), it was observed that such over-segmentation was not always present in chronic constipation. The present study is an attempt further to investigate sigmoid motor abnormalities in chronic constipation. On the other "Address for correspondence and reprints requests: Dr P. Meunier,