Tetanus antibody determinations in 109 children aged 1 1/2 to 15 1/2 years showed that 98.2% had a sufficiently protective tetanus antitoxin titre. There were no significant differences between completely and incompletely first immunised children. Increased titres of up to 25 IU/ml serum were found shortly after multiple boostering. According to the observed titres boostering after trauma is at the earliest necessary after 5 years in complete or incomplete primary immunisation or after the last boostering. Passive immunisation is only indicated in the traumatised non-immunised and in patients with wounds of larger standing who have not been immunised for more than 5 years.