1 To study the effect of drugs on methods of assessment of gut transit time a double-blind study of the effect of single doses of placebo, oxyphenisatin, anthracene purgatives, (+)-norpseudoephedrine and a combined preparation of (+)-norpseudophedrine and senna was carried out in ten normal volunteers. Gut transit time was assessed by dye and radio-opaque marker methods. 2 It was possible to demonstrate the effect of the anthracenes but not oxyphenisatin on gut transit time. 3 More sophisticated statistical techniques were required to demonstrate the retarding effect of the sympathomimetic amine and its reversal by senna. 4 Statistical analysis shows that assessment of intestinal transit time by dye or pellet methods gives identical information.