BACKGROUND AND OBJECTIVES We report the results of a study using a recombinant DNA HBV vaccine in newborns from an endemic area for HBV and compare the anti-HBs kinetics with observations in adults in order to make estimates about the need for booster vaccinations. STUDY DESIGN One hundred and forty-eight neonates were vaccinated and followed for 62 months. Based on the presence or absence of hepatitis B surface antigen in the mother, cohorts of 'exposed' and of 'non-exposed' neonates were identified. RESULTS A maximum concentration is normally observed after the booster vaccination followed by a rapid decline. According to Ambrosch et al. and Gesemann et al., titer calculations as a function of time, yielded 37 IU/1 and 47 IU/1 at month 60 respectively. The mean titer for the three groups of neonates investigated was at that time 74 IU/1. The prospective time intervals to arrive at an anti-HBs level of at least 10 IU/1 can be individually calculated from the individual titer after the booster vaccination. These calculated estimates show respectively: that 8.3% of the vaccinated neonates need a new booster vaccination within 14 months; that 26.7% will need a new booster within 50 months; and that only 65% need a new booster in 50 or more months. CONCLUSION It can be concluded that anti-HBs kinetics in very young children and adults are comparable. The least expensive way of maintaining protection against HBV in neonates seems to be the determination of the individual titers after the first booster vaccination and calculation of the prospective time interval to arrive at a minimum titer of 10 IU/1 and the need for a new booster vaccination.