There is mounting evidence that the imbalance between Th1 and Th2 lymphocyte subsets plays a key role in the development of autoimmune diabetes in NOD mice, but it is also possible in humans. The aim of the present study was the estimation of in vitro production of Th1 (INF-gamma, IL-2) and Th2-derived (IL-4, IL-10) cytokines by peripheral blood in ICA and GADA positive first degree relatives of Type-I diabetes patients, since they could represent primary events triggering an immune-mediated islets destruction. The study was performed in 25 subjects at risk of insulin-dependent diabetes and 21 age- and sex-matched healthy controls. Cytokine levels in supernatants of whole blood cultures with PHA (10 microg/ml) were quantified by ELISA. We observed a lower concentration of IL-4 in culture supernatants in ICA and GADA positive relatives as compared with the control group, both at 48 h and at 72 h of incubation. Similarly, in the prediabetic group, lower IL-10 levels at 48 and 72 h of culture were found. We did not observe statistical differences in in vitro production of IL-2 and INF-gamma by peripheral blood in high risk diabetes mellitus subjects and healthy controls. In subjects at increased risk of Type-I diabetes, levels of IL-4 positively correlated with those of IL-10. There were negative correlations between IL-10 concentration after 48 h of incubation and levels of HbA1C. In conclusion our study has shown decreased IL-4 and IL-10 production, but normal secretion of Th1-derived cytokines by peripheral blood of prediabetic humans. This could suggest that the early stage of autoimmune process in Type-I diabetes in humans is associated with decreased function of Th2-cells rather than overactivation of Th1 subset in the peripheral blood.