SUMMARY1. The ureter of the domestic pig was examined histologically. The muscle coat does not have two distinct layers: probably there is a spiral arrangement of a single muscle coat.2. Even with specialised stains there was no sign of a plexus of nerve fibres and cells as in the niyenteric plexus of the gut: nerve fibres were seen only in the adventitia.3. The ureter of the pig lends itself to studyin vitroin Trendelenburg's apparatus.4. Acetylcholine has a powerful motor action easily abolished by atropine.5. Noradrenaline and adrenaline are also powerfully motor in action. In the presence of phenoxybenzamine this motor effect is abolished and replaced by inhibition.6. lsoprenaline is inhibitor and this inhibition is abolished by pronethalol.7. There seem therefore to be α and β adrenergic receptors in ureter.8. In the discussion there is speculation about the significance of such findings for an explanation of vesico‐ureteric reflux in