Using the second generation ELISA test, we studied the prevalence of antibodies against hepatitis C virus (anti-HCV) among 159 household contacts of 86 anti-HCV positive subjects (index cases). Fourteen (8.8%) relatives were found anti-HCV positive, a rate higher than the corresponding figure reported among the general population in the same area. The prevalence of anti-HCV was significantly higher among sexual partners than among household contacts without sexual relations with the index case (18% vs. 3.1%; P < 0.01). These findings indicate that sexual transmission may be the main route for intrafamily HCV spread.