Human immune globulin (IG) 10 % liquid (Gammagard Liquid®) is a ready-to-use, highly purified, and concentrated immunoglobulin (Ig)G solution approved in the US for both intravenous and subcutaneous antibody replacement therapy in patients aged ≥2 years with primary humoral immunodeficiency. Intravenous IG 10 % liquid every 3-4 weeks for ≥12 months, at median serum IgG trough levels of 9.6-11.2 g/L, completely prevented acute serious bacterial infections (SBIs) in a phase III clinical trial. Weekly subcutaneous IG 10 % liquid at a dose equal to 137 % of the equivalent weekly intravenous dose, which was earlier determined to produce the same IgG exposure, produced higher serum trough IgG levels and lower peak IgG levels than intravenous administration, and also effectively reduced SBIs; the infection rate was 0.067 SBIs/subject/year, which met the US FDA efficacy criterion of <1 SBI/subject/year. The rates for non-serious infections of any kind were low for both intravenous and subcutaneous therapy. Both intravenous and subcutaneous IG 10 % liquid were safe and generally well tolerated. Systemic adverse reactions were more frequent with intravenous therapy and local infusion-site reactions were more frequent with subcutaneous therapy, but the latter reduced over time. Most adverse reactions were of mild or moderate intensity. Thus, IG 10 % liquid is an effective and generally well-tolerated preparation for both intravenous and subcutaneous IgG replacement therapy in patients with primary immunodeficiency disorders involving antibody deficiency. It offers the benefits of a ready-to-use, liquid preparation and the convenience of home-based therapy in appropriate patients.