Measurement of segmental colonic transit is important in the assessment of patients with severe constipation. (111)ln-diethylenetriamine pentaacetic acid (DTPA) has been established as the tracer of choice for these studies, but it is expensive and not readily available. Ga-67-citrate is an inexpensive tracer and when given orally is not absorbed from the bower. It was compared with (111)ln-DTPA in colonic transit studies in nonconstipated control subjects and then in patients with idiopathic constipation. Methods: Studies were performed after oral administration of 3 MBq (81 mu Ci) Ga-67-citrate or 4 MBq (108 mu Ci) (111)ln-DTPA in solution. Serial abdominal images were performed up to 96 h postinjection, and computer data were generated from geometric mean images of segmental retention of tracer, mean activity profiles and a colonic tracer half-clearance time. Results: There were no differences in segmental retention of either tracer or in mean activity profiles between control subjects and constipated patients, Results in constipated subjects were significantly different from those in controls. The mean half-clearance times of tracer for control subjects were 28.8 h for Ga-67-citrate and 29.9 h for (111)ln-DTPA in control subjects and 75.0 h for Ga-67-citrate and 70.8 h for (111)ln-DTPA in constipated patients. Conclusion: Oral Ga-67-citrate can be used as a safe alternative to (111)ln-DTPA for accurate measurement of segmental colonic transit.