The motility in the first part of the duodenum has been studied by a method combining roentgen fluorography and multiple pressure recordings in 7 normal volunteers, in 7 patients having gastric, and in 7 having duodenal, ulcer. A significantly lower number of retrograde motor sequences was found in cases with duodenal ulcer than in normals, while patients with gastric ulcers showed no such difference. This abnormality in subjects with duodenal ulcer was interpreted as a deficiency in the transport of neutralized duodenal contents from more distal parts of the duodenum up into the bulb. The abnormality can explain the earlier known lower pH in the duodenal bulb in subjects with duodenal ulcer and contribute to the pathogenesis of the disease.