The range of diseases in which intravenous immunoglobulin (IVIG) is effective has expanded significantly since its initial use in primary antibody deficiency. There are at present at least 17 preparations of IVIG in use worldwide with similar profiles of adverse effects. Infusion-related effects range in severity. Mild adverse reactions (headache, flushing, low backache, nausea, wheezing) are often associated with a fast infusion rate, and respond rapidly on slowing the infusion. Very rare episodes of life-threatening anaphylaxis may occur, particularly in those IgA-deficient patients with anti-IgA antibodies; such patients should receive an IgA-depleted preparation of IVIG. There are concerns with any blood product about safety in regard to viral transmission. The 4 outbreaks of non-A non-B hepatitis (probably hepatitis C) in the 1980s were associated with the use of particular batches of IVIG. The more recent exclusion of all anti-hepatitis C virus positive individuals from the donor pool, and the introduction of specific antiviral steps in the manufacture of IVIGs, should prevent further outbreaks. The human immunodeficiency virus (HIV) is effectively inactivated during the manufacturing process itself and HIV transmission has not been reported with IVIG. Rarely, haematological (Coombs' test positive haemolysis), neurological (aseptic meningitis) or renal (transient rises in serum creatinine) adverse effects may be seen when high doses of IVIG are used for immunomodulatory purposes. Haemolysis, due to passive transmission of blood group antibodies (anti-A, anti-D), may be prevented by selecting IVIG batches that give a negative cross-match between the recipient's red cells and IVIG.(ABSTRACT TRUNCATED AT 250 WORDS)