Intravenous immune gammaglobulin (IVIgG) has a definite role in the modern armamentarium of therapies for immunocompromised patients. Intravenous IgG is manufactured from the plasma of a large number of donors and contains antibodies against numerous infectious agents. Patients who receive infusions of IVIgG may test false-positive for a variety of viral, bacterial, and other infectious diseases when serologic determinations are performed on their blood samples. It is important that laboratories performing serologic testing be aware that patients have been infused with IVIgG, so that spurious laboratory results can be identified. Serologic testing on implicated lots of IVIgG and on the patient's pretreatment sample may aid in correctly identifying a spurious serologic result due to therapy with IVIgG.