Intravenous immunoglobulin (IVIG) has been used to treat many autoimmune disorders including Stiff-Man Syndrome (SMS). SMS is a neurological disorder associated with an immune-mediated deficiency of gamma-aminobutyric acid (GABA) due to autoantibodies against the GABA synthesizing enzyme glutamic acid decarboxylase-65 (GAD65). GAD65 autoantibodies are present among 1-2% of healthy individuals. It can therefore not be excluded that GAD65 autoantibodies may be present in IVIG, which is prepared from multiple blood donors. We report here that GAD65 but not IA-2 autoantibodies were present in commercial IVIG preparations. The presence of autoantibodies may affect the outcome of IVIG treatment and screening commercial preparations of IVIG for GAD65 autoantibodies is therefore recommended before treating patients.