Anti-HCV antibodies were detected in 11 children undergoing BMT. All of them had received intravenous immunoglobulins (Ig) at a dose of 500 mg/kg every 2 weeks for the first 100 days post-BMT. Antibody titers appeared after the first dose and became undetectable between 1 and 6 months after the last dose of Ig. Detection of anti-HCV antibodies in these multitransfused patients raised doubts about their clinical significance. The clearance of antibody titers in the ensuing months, negativity of HCV RNA in the serum of the patients and the presence of anti-HCV in some batches of the commercial preparations administered supported the diagnosis of a passive transfer of antibodies and that true HCV infection could be ruled out. Routine screening of donors with the most sensitive tests and exclusion of anti-HCV positive sera from plasma pools should be mandatory. The presence of anti-HCV in these products has important clinical implications, leading to more expensive and time-consuming diagnostic procedures.