The use of small portable pumps for subcutaneous infusion of IgG in patients with primary immunodeficiencies was introduced more than 20 years ago. In the US, i.v.i.g. became more popular, but in other countries, many patients use the subcutaneous route. Pharmacokinetics of IgG differ when smaller doses are given more frequently, as is commonly done with subcutaneous regimens, as compared to the large boluses given every 21-28 days in most i.v. regimens. Differences include lower peaks and higher troughs, which may be preferable for some patients. Advantages of the subcutaneous route include increased patient autonomy, decreased systemic adverse effects, and the lack of a requirement for vascular access. Disadvantages include limitation in the volume that can be administered at any one time, necessitating frequent dosing; and the requirement for reliability if a patient is to self or home infuse. Obstacles may be encountered because no preparation of IgG is currently licensed for subcutaneous use in the US. Subcutaneous IgG replacement may be preferable to i.v. infusions or i.m. injections for carefully selected patients.