The dumping syndrome is the commonest cause of distress after partial gastrectomy, and may also occur after total gastrectomy, after gastro-enterostomy, and after pyloroplasty. For many years it has been known that if patients with this syndrome drink a hypertonic solution of glucose their usual post-cibal symptoms will be provoked (Machella, 1949 al., 1960), and this observation was later repeated with a similar nmeal preceded by a suitably adjusted dose of insulin. On each occasion the test was performed between 8 and 9 a.m., with the patient sitting at a table, having taken nothing by mouth for the previous 12 hours. A precisely similar meal was served to each patient. In five instances, at the first test the patients were persuaded and cajoled into eating as much as they possibly could, despite the onset of symptoms which would normally have caused them to stop eating: fro.m the amount of food left their intake was then calculated, and at the second test they were given exactly what they had eaten on the first occasion. The other two patients were allowed to eat as much as they wanted on each occasion.The results are set out in detail in Table I. In all seven patients the first meal provoked marked typical dumping symptoms, whereas after the second meal these symptoms were either absent or greatly reduced. In all seven patients the fall in plasma volume after the second meal was smaller than after the first (t=7.95; P