According to these data, when a vaccine schedule includes five doses, the prevalence of unprotected subjects is only 3·1%; if the number of doses was >5, no one was found to be unprotected. Relationships between intervals since the last vaccine dose, number of vaccine doses and percentage of unprotective titres in subjects who received tetanus vaccines Interval since last dose (years) Frequency of unprotected subjects Per cent Frequency of unprotected subjects after five doses Per cent Frequency of unprotected subjects after more than five doses Per cent Doses: mean (s.d.) els5 0/415 0 0 0 0/415 0 5·49 (0·84) 6-els10 1/42 0·2 1/42 0·2 0/42 0 5·36 (0·69) 11-els15 14/241 5·8 5/241 2·1 0/241 0 4·61 (0·71) >15 57/355 16·1 16/355 4·5 0/355 0 4·42 (0·66) Columns 2, 3 and 4 are published in 1. According to our results, this should provide protection for a long period of time.