Intravenous immunoglobulin (IGIV) replacement therapy is the standard of care for primary immunodeficiencies with impaired humoral immunity. It is also the immunomodulatory therapy of choice for some types of neuroimmunologic and autoimmune hematologic disorders and for immunomodulation in bone marrow and some solid organ transplants. Currently available IGIV products include older lyophilized formulations, 5% liquid products, and newer, liquid, ready-to-use, 10% formulations. Differences in the formulations, manufacturing processes, excipients, pH, and other physicochemical properties of IGIV products may affect their clinical efficacy and tolerability. Among at-risk patients, the possibility of serious complications such as renal insufficiency, heart failure, thrombotic events, and immunological reactions may be increased if an IGIV formulation has sugar as a stabilizer, has high sodium or immunoglobulin A (IgA) content, or is hyperosmolar. The 10% liquid formulations may offer advantages because of their lower IgA concentrations, optimal pH, glycine or proline stabilizers, low sodium content, and lower osmolality. Liquid formulations are more convenient for patients and health care providers due to shorter infusion times and easier preparation and administration.