Lymphocyte activation was examined by interleukin-2 (IL-2) receptor expression on peripheral blood mononuclear cells from coeliac and control subjects. Purified T cells were incubated with gluten fraction 111 (a known toxic peptide for coeliac subjects), soyabean hydrolysate (an unrelated hydrolysed food antigen), and Concanavalin-A (Con-A, a non-specific mitogen). After 1-5 days incubation, expression of IL-2 receptors was assessed using a cellular enzyme-linked immunosorbent assay (ELISA). Gluten fraction 111 induced expression of IL-2 receptors on T lymphocytes from coeliac but not from normal subjects (P = 0.0005), whereas soyabean hydrolysate did not induce IL-2 receptor expression. Lymphocytes from both coeliac and normal subjects had similar increased IL-2 receptor expression after incubation with Con-A. Flow cytometry was also used to confirm specific expression of IL-2 receptor expression of lymphocytes from coeliac subjects. Interleukin-2 receptor expression increased from 0 to 5.4% of cultured mononuclear cells after 7 days incubation with gluten fraction III. These cells were CD3-positive and CD4-positive. We conclude that peripheral blood lymphocytes from coeliac subjects are sensitized specifically to gluten fraction III.