BACKGROUND The efficacy of the treatment of patients with chronic idiopathic constipation not responding to normal therapeutic measures depends on correct functional diagnosis. The study of the segmentary and total colonic transit time with radioopaque markers is the most economic technique in everyday clinic ambience for functionally evaluating these patients. METHODS Segmental and total colonic transit time was calculated with the use of radioopaque markers in 23 healthy subjects (12 men and 11 women) and in 13 women with severe idiopathic constipation. Twenty markers were administered daily for three consecutive days and simple x-rays of the abdomen were made on the fourth, seventh and in some cases on the tenth day. In addition, the symptomatology of 9 patients was collected by means of a 30 day diary. RESULTS The maximum values of transit time (mean + 2SD) obtained in the healthy subjects were 17, 25, 26, and 49 hours for the right colon, left colon, rectosigmoid and the whole colon, respectively. The time of left colon transit was significantly lower in the women. The transit time in constipated patients permitted the differentiation of three functional patients: a) slowing of the right and left colon possibly associated to rectosigmoid slowing in 5 patients; b) isolated slowing in the left colon in 4 patients and c) isolated rectosigmoid slowing in 4 patients. Group a) was characterized by long total colonic transit times while these were normal in 2 patients of group b) and in one patient of group c). No differences were seen in the symptomatology of the groups. CONCLUSIONS The calculation of segmentary and total colonic transit time with radioopaque markers is a simple technique which permits the detection of different subgroups of patients with chronic idiopathic constipation refractory to normal treatment. The exact typification of the functional anomaly is an important basis for the individualization of treatment.