The clinical and serological course of a haemophilic baby who was transfused with 160 ml of blood containing the hepatitis C virus (HCV) (0.70 Meq. ml-1) on the sixth-post-natal day is described. He is the infant of an HCV-negative mother. One month after the transfusion, there was a marked increase in HCV RNA and a small amount of HCV antibody was detected. This case provides evidence that a newborn is capable of producing HCV antibodies.