Evidence for cow's milk allergy was looked for prospectively in 15 children with recurrent vomiting. Whereas radiological examination showed gastro-oesophageal reflux to be present in all patients, 3 out of 15 children presented an enteropathy associated with an increased number of IgE plasmocytes in small intestinal biopsy tissue. These three patients did not improve with conventional medical therapy but a striking improvement occurred within 24 h on a cow's milk-free diet. We conclude that diagnostic confusion between gastro-oesophageal reflux and cow's milk allergy can occur and that the presence of IgE plasmocytes in small intestinal biopsy tissue indicates IgE-mediated cow's milk protein allergy. All cases of "intractable" gastro-oesophageal reflux should be suspected of cow's milk allergy and investigated accordingly.