In this study, different intravenous immunoglobulin infusions (I.V. Ig.), were analyzed for the presence of either anti-HLA antibodies (Ab1) or anti-idiotypic antibodies (Ab2) directed against Ab1 anti-HLA. No evidence of either antibody types was found in tested I.V. Ig. preparations. Because of the absence of Ab1 anti-HLA, prophylactic and/or therapeutic use of I.V. Ig. appears safe in patients waiting for organ graft or in transplanted patients. The lack of Ab2 anti-Ab1 anti-HLA makes worthless the utilization of such preparations for neutralization of Ab1 present in highly sensitized dialysis patients or suppression of their production in transplanted patients in contrast with the previous reports suggesting this possibility.