Leucocyte migration inhibition in response to challenge with gluten fraction III was prevented by pretreatment of coeliac leucocytes with pronase, an enzyme that removes cytophilic antibodies. Leucocytes from healthy volunteers preincubated with serum from untreated and treated coeliac patients showed marked migration inhibition when incubated with gluten fraction III. No migration inhibition was observed with leucocytes from healthy volunteers preincubated with serum from patients with small bowel diseases other than coeliac disease and from other healthy volunteers. Untreated and treated coeliac patients who were leucocyte migration inhibition negative in the direct assay had migration indices in the sensitized range in the serum induced assay. This work is in keeping with a previous suggestion that in coeliac disease leucocyte migration inhibition induced by gluten fraction III is caused by cytophilic antibodies.