The clinic records of 1,009 women, aged greater than or equal to 28, who comprised the entire cohort of the six kibbutzim studied, were reviewed concerning basic tetanus immunization and booster injections. Immunization was incomplete in 6.5% of women aged 28 to 39 years (the youngest age-group), 13.7% in those aged 40 to 49, 55% in the 50 to 59 year age-group, and 68.2% in those aged greater than or equal to 60. There were no significant differences between the age-groups regarding the number of booster doses given. Blood samples drawn at random from 120 of the women whose records were surveyed (30 from each age-group) showed that all had a protective titer of antibody to tetanus toxin as determined by the passive hemagglutination method: 15 of them (12.5%) had never received basic immunization or a booster dose. Whatever the method chosen for determining immunity--chart review or antibody titer--the level of protection was lower in the older age-groups. The implications of this finding for future immunization programs, and the possibility that there may be widespread, acquired natural immunity to tetanus in rural communities, are discussed.