The 1996 production halt of adenovirus types 4 and 7 vaccines prompted concerns about the resurgence of large respiratory disease outbreaks among US military basic trainees. This serosurvey was conducted to assess the current susceptibility of the trainee population to these viruses. A stratified, random sample (n=303) of trainees' sera was tested using a quantitative colorimetric microneutralization assay to demonstrate antibody titers considered to provide immunologic protection against each adenovirus type. Results were analyzed for relationships between susceptibility and 4 demographic factors-gender, race, prior military service, and age. Results showed that 66% and 73% of trainees were susceptible to serotypes 4 and 7, respectively. Nearly 90% were susceptible to at least one serotype. Susceptibility was significantly (P<.05) related to lack of prior military service and younger age. Consistent with a serosurvey conducted 20 years ago, these results demonstrated significant susceptibility to two vaccine-preventable causes of disease. These findings may have civilian implications.