The prevalence of both the hepatitis-B surface antigen (HBsAg) and its specific antibody (anti-HBs) was significantly greater in the sera of White patients suffering from sexually transmitted diseases than that in White blood donors. However, Black patients with venereal diseases did not show an increased prevalence of either HBsAg or anti-HBs. These findings support the view that heterosexual transmission of the hepatitis-B virus is less likely to occur in populations in whom this infection is largely acquired before the age of sexual maturity.