A pair of correspondent adhesion molecules: LFA-1 (CD11aCD18) and ICAM-1 (CD54) was shown to be involved in autoimmune insulitis in animal models. Anti-LFA-1 or anti-ICAM-1 monoclonal antibodies administered in vivo had a very strong preventive effect on the development of spontaneous diabetes with a marked reduction of insulitis. On the other hand elevated levels of the soluble form of ICAM-1 (sICAM-1) were documented in subjects at risk for type 1 diabetes. Recently sICAM-1 was shown to play an immunoregulatory role as an inhibitor of islet insulitis. The aim of the present study was to evaluate CD11a + mononuclear cells (lymphocytes and monocytes) and soluble sICAM-1 levels in the peripheral blood of subjects with preclinical and overt type 1 diabetes to assess their role in the development of the autoimmune process and their possible associations with the humoral autoimmune markers. The study was carried out in three groups of subjects: 26 first degree relatives of type 1 diabetes patients (prediabetics) with the combinations of autoantibodies against pancreatic B cells (ICA, GADA, IA-2A, IAA), 22 patients with a recent onset of type 1 diabetes and age and sex-matched 24 healthy volunteers (control group). We observed an increased fluorescence intensity of CD11a on mononuclear cells in overt diabetes subjects and a positive correlation between CD11a fluorescence intensity on monocytes and ICA titre. The highest sICAM-1 levels we obtained in the peripheral blood in the prediabetics in comparison to patients with clinical diabetes and the healthy controls. We found a positive correlation between slCAM-1 and values of ICA, GADA and a total number of antibodies present. In conclusion our study suggests that LFA-1 and sCAM-1 play an important role in the pathogenesis of type 1 diabetes. The assessment of the CD11a bearing monocytes and sICAM-1 levels are potential markers of the preclinical stage of the autoimmune diabetes, but further prospective studies in high risk diabetes type 1 subjects are needed.