The courses of 18 children born to 13 chronic hepatitis B surface antigen (HBsAg) carrier mothers were followed prospectively for serological and biochemical evidence of type B hepatitis. Three children developed transient HBsAg positivity accompanied by the appearance of antibody to the hepatitis B core antigen. Two others had no detectable HBsAg but developed antibody to HBsAg. These serological manifestations of hepatitis B virus infection occurred late--6 to 24 months after birth. None of the children had clinical evidence of hepatitis and none became chronic HBsAg carriers. The infrequency of transmission of infection, the mild course of disease, and the lack of persistence of HBsAg in these children probably reflected the low level of infectivity of the chronic carrier mothers and perhaps the healthy immunologic status of the children.