This is an open-label, multicenter, phase 4 study in IG treatment-naïve participants with PID, conducted in the United States (US), to assess the PK, safety, and tolerability of IgPro20. The primary objective of this study is to characterize the PK of IgPro20 and to assess the safety and tolerability of IgPro20 in IG treatment-naïve participants with PID who are aged greater than or equal to (>=) 18 years.

Inclusion Criteria:

• - Participants must be aged >=18 years.
• - Participants must have a confirmed and documented diagnosis of PID, must be IG treatment-naïve and have an IgG level less than or equal to (<=) 400 milligrams per deciliter(mg/dL) at Screening.

Exclusion Criteria:

• - Participants with hyperprolinemia.
• - Participants who are receiving the following medications:
• • Systemic corticosteroids (prednisone or equivalent; average daily dose of greater than [>] 15 mg) from 4 weeks before Screening.
• • Any dose of systemic immunosuppressants within 9 months or 5 times the half-life (t½) plus 6 months before Screening, whichever is longer.
• • Any dose of biologic therapies with influence on the immune system (eg, tumor necrosis factor inhibitors, interleukin inhibitors, B-cell inhibitors), including investigational agents, within 12 months or 5 times the t½ plus 6 months before Screening, whichever is longer.
• • Participants who are currently receiving anti-coagulation therapy.
• - Participants with hypoalbuminemia, protein-losing enteropathies, and kidney diseases with proteinuria.
• - Participants with a documented history or a current diagnosis of a thromboembolic event(s) (eg, deep vein thrombosis, pulmonary embolism, myocardial infarction, cerebrovascular accident, transient ischemic attack) or coagulopathy within 12 months before Screening.
• - Participants with severe dehydration and known blood disorders affecting viscosity.
• - Participants with aspartate aminotransferase and alanine aminotransferase concentration > 3 times the upper limit of normal (ULN; central laboratory) at Screening.
• - Participants with creatinine concentration > 1.5 times the ULN (central laboratory) at Screening.
• - Participants with new onset or worsening or severe cardiac, pulmonary, kidney disease, and liver disease.
• - Participants with malignancies of lymphoid cells such as chronic lymphocytic leukemia, non-Hodgkin's lymphoma, and immunodeficiency with thymoma.

CSL will consider on a case-by-case basis requests to share Individual Patient Data (IPD) with external bona-fide, qualified scientific and medical researchers. For information on the process and requirements for submitting a voluntary data sharing request for IPD, please contact CSL at clinicaltrials@cslbehring.com.

Requests for IPD will generally be considered once review by major regulatory authorities (ie FDA, EMA) is complete and the primary publication is available.

Proposed research should seek to answer a previously unanswered important medical or scientific question.

Applicable country specific privacy and other laws and regulations will be considered and may prevent sharing of IPD.

If the request is approved and the researcher has executed an appropriate data sharing agreement, IPD that has been appropriately anonymized will be available.