Additional Study Information: Subjects with Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) will be enrolled in the study and Intravenous Immunoglobulin (IVIg) will be given to eligible subjects on the study. CIDP is a chronic inflammatory condition that causes the immune system to attack the nerves. IVIg is one common treatment for CIDP. IVIG is a blood product that is administered by an infusion nurse. For CIDP, IVIg is usually administered every 3 to 6 weeks. The CIDP doctor will decide how often you receive IVIg. This study is being done because we do not understand how symptoms of CIDP fluctuate (for example, wearing-off of IVIg) in between these IVIg infusions. CIDP symptoms may include weakness, numbness, pain, or difficulty walking. The goal of this study is to better understand how your CIDP symptoms change in between IVIg treatments. We hope that this information will help doctors be better able to treat patients like you with CIDP.