Hepatitis B virus (HBV) infection is endemic among institutionalized retarded patients, who usually have mild, anicteric hepatitis following nonparenteral exposure. We evaluated the risk of HBV infection (as evidenced by serologic studies) among their contacts, including noninstitutional caretakers, during brief home exposure. Caretakers shaved, bathed, and changed diapers for five patients during home visits or foster home placements. Seven of the 14 caretakers, who were exposed for 3–12 months, developed antibodies (anti-HBeand/or anti-HBs). A mother and her daughter's caretaker were found to have asymptomatic acute HBV infection, and the mother developed antibodies to HBsHBc, and HBc. In a second household, another caretaker became anti-HBspositive. Only one of nine play contacts and none of seven casual contacts had markers of past or present HBV infection. The study was a unique opportunity to retrospectively and prospectively monitor HBV transmission. Our results show that noninstitutional caretakers deserve the protection of HBV vaccine to diminish the potential for chronic infection and transmission of HBV infection.