Subjects who have completed subcutaneous (SC) Week 25 or were successfully rescued from a CIDP relapse during the SC Treatment Period of pivotal study IgPro20_3003 (NCT01545076) will have the option to receive open-label low-dose IgPro20 (0.2 g/kg bodyweight [bw]) weekly for up to 48 weeks. Subjects relapsing on low-dose IgPro20 will either return to high-dose IgPro20 (0.4 g/kg) immediately or be discontinued, depending on investigator's judgment. Subjects returning to high-dose IgPro20 will continue on high-dose until they have completed a total of 48 weeks of IgPro20 treatment. If subjects do not successfully recover from CIDP relapse within 4 weeks, they will be withdrawn.