This study investigates whether military records can be used to identify US Army Vietnam veterans who were likely to be exposed to the herbicide Agent Orange. Serum levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a toxic contaminant in Agent Orange, were obtained for 646 ground combat troops who served in heavily sprayed areas of Vietnam and for 97 veterans who did not serve in Vietnam. The distributions of current TCDD levels in Vietnam and non-Vietnam veterans were nearly identical (mean in each group, ≈4 parts per trillion [ppt]). Only two men (both Vietnam veterans) had clearly elevated levels (>20 ppt). Levels of TCDD did not tend to increase with greater likelihood of exposure to Agent Orange, as estimated from either military records or self-reported exposure. This study is consistent with other studies and suggests that most US Army ground troops who served in Vietnam were not heavily exposed to TCDD, except perhaps men whose jobs involved handling herbicides.