Four patients (2 with X-linked, one with common variable hypogammaglobulinaemia, and 1 with ulcerative colitis) developed non-A, non-B hepatitis (NANBH) following administration of a specific batch of intravenous immunoglobulin (IV IgG) manufactured by the Scottish National Blood Transfusion Service using the pH4/mild pepsin method. Each patient had normal serum ALT levels over a preceding period of 12-67 months, with raised values developing within 4-18 weeks of first administration of the implicated batch. Two patients had very mild symptoms of hepatitis, the other 2 being asymptomatic. Over a follow-up period of 8-12 months, ALT levels returned to normal in 3 patients, but biopsy-proven chronic NANBH developed in the fourth. The level of NANBH virus in the starting plasma used to manufacture this batch may have exceeded the capacity of the process to inactivate the virus. The transmission of NANBH by one of approximately 110 batches administered demonstrates the importance of continued close surveillance of recipients of IV IgG, even if asymptomatic, by regular monitoring of liver function tests and recording of all batches received.