A case is reported of a 43 year old man who suffered from a grass pollen allergy and a malabsorption syndrome and in whom a paraproteinaemia was found. The grass pollen hypersensitivity was abolished by desensitization. The malabsorption syndrome was found to be due to coeliac disease--that is, a "flat" mucosa of the jejunum with an almost normal ileal mucosa--followed by clinical recovery and morphological improvement on a gluten-free diet. A short period of gluten reintroduction caused deterioration of the jejunum. The monoclonal immunoglobulin (IgG-gamma) diminished and disappeared in the course of three years. Although it has not been possible to demonstrate that this paraprotein had anti-gliadin activity, it is suggested that the constant stimulation of the gut reticuloendothelial system by gluten might bear some relation to the appearance of the paraproteinaemia.