Objective: Chewing leaves of the qat plant (Catha edulis) for their pleasurable central stimulant effect is a habit widespread in the Yemen and central areas of East Africa. Their use is believed to cause a variety of gastrointestinal symptoms including constipation. We studied the effect of chewing qat leaves on whole gut transit time. Methods: A prospective study in 10 healthy volunteers studied on 2 occasions a week apart. The subjects either chewed qat 3 hours daily for 7 days or abstained from chewing qat for 7 days before the whole gut transit time measurement. Whole gut transit time was measured using the radio-opaque maker's technique. Results: the whole gut transit time was significantly (P=0.00255) prolonged during the qat arm compared to the control arm of the study. There was also a significant (P=0.00585) hardening of the stools during the qat chewing arm as expressed by a lower score on the Bristol stool form scale. Conclusions: We have confirmed by objective measurement that qat chewing slows the whole gut transit time. This effect is believed to be caused by the sympathomimetic action and cathinone and cathine and the astringent properties of tannin in qat leaves.