In Sweden, 44 patients were reported to have contracted hepatitis C virus (HCV) infections from treatment with intravenous immunoglobulin. Gammagard was the product implicated in HCV transmission in 12 patients; 8 of these 12 patients were HCV ribonucleic acid (RNA)-negative during the 2 years before Gammagard was administered and 10 showed clustering by sequencing of the HCV core gene. Further studies are being conducted to correlate the sequenced HCV RNA with specific batches of Gammagard. Nine patients who received Gammonativ in 1983 and 1984 had a strong time-related possibility of HCV infection. Sequencing analyses are being performed in these patients as is being done for the patients who received Gammagard. Another 21 patients who received Gammonativ from 1982 to 1985 are probably infected with HCV, but confirmation of implicated batches is lacking. The association between Sandoglobulin and HCV is questionable in two patients, although plausible because of a time relationship. In Norway, relationships between Gammonativ and the incidence of HCV infection are similar to those in the 21 sporadic cases in Sweden. Also in Denmark and Finland, HCV infection appears to be related to the lack of additional viral inactivation steps used in the preparation of intravenous immunoglobulin. Clearly, there is a need for increased antiviral inactivation and antiviral screening in the production of intravenous immunoglobulin products.