In autoimmune disease the functional deficiency of T suppressor cells, also described in Type I diabetes, may be restored through immunoglobulin (Ig) infusion, which increases antigen phagocytosis, NK activity, cell clones and antibody anti-idiotype responses. Sixteen Type I diabetic patients were studied: eight were treated soon after the initial correction of disease-onset glycemic deterioration with intensive intravenous (i.v.) 7S Ig treatment (0.4 g/kg/BW) for 1 week and once per week for 6 months, whilst the remaining patients constituted the control group. All patients were evaluated during the study for metabolic and immunological parameters. A reduction in insulin requirement compared to conventionally treated patients was observed at the third (0.17 +/- 0.06 vs 0.44 +/- 0.08 IU/kg/BW; P less than 0.02) and at the sixth month of therapy (0.19 +/- 0.07 vs 0.54 +/- 0.07 IU/kg/BW; P less than 0.005). Two patients ceased to require insulin therapy within the BW; P less than 0.005). Two patients ceased to require insulin therapy within the first month, showing a prolonged restoration of B-cell function. Serum C-peptide values were also significantly higher in the Ig-treated group compared to the control group after 3 and 6 months. As regards immunological parameters, patients showed a decrease in insulin antibody levels and a reduction in TAC+ cells. Intravenous Ig therapy seems able to affect positively the first phases of metabolic and immunological deterioration of Type I diabetes.