On Nov. 22, 1991, the Immunization Practices Advisory Committee (ACIP) published recommendations for routine hepatitis B vaccination for all infants in MMWR. The vaccination schedule most often used for adults and children has been three intramuscular injections, the second and third administered 1 and 6 months, respectively, after the first. An alternate schedule of four doses has been approved for one vaccine that would allow more rapid induction of immunity. However, for preexposure prophylaxis, there is no clear evidence that this regimen provides greater protection than that obtained with the standard three-dose schedule.