We have prospectively examined the percentage of peripheral blood lymphocytes which expressed adhesion molecules in untreated Graves' disease patients. Eighteen patients with Graves' disease, twenty-four patients with Hashimoto's thyroiditis and thirty-two sex- and age-matched healthy control subjects were studied. The expression of the lymphocyte adhesion molecules beta-1 integrin CD29, beta-2 integrin CD11b and L-selectin Leu8 (CD62L) was analyzed by cytofluorometry. A decreased percentage of CD29+ and CD11b+ lymphocytes was observed in hyperthyroid patients in comparison with Hashimoto's thyroiditis patients and healthy controls. However, there was no difference in the percentage of CD62L+ lymphocytes in the three groups. Percentages of lymphocyte activation markers, hyperthyroid status, presence or absence of ophthalmopathy or serum levels of antithyroid antibodies were not related to the proportions of CD29+ or CD11b+ lymphocytes. Four Graves' patients required radical therapy but after the treatment, there was no modification in the percentages of CD29+ and CD11b+ lymphocytes compared with those determined at diagnosis. Our findings suggest that the decrease in beta-1 and beta-2 integrins could be a predisposing marker of development of Graves' disease.