service connection (see Box 1-1). The 1991 legislation also asked the National Academy of Sciences, through the IOM, to conduct periodic reviews of the scientific and medical evidence connecting certain herbicide exposures to health effects. The IOM issued its first VAO report in 1994; the latest report, Veterans and Agent Orange, Update 2008, was published in 2009.

Before 1997, Vietnam veterans were eligible for a presumption of exposure to any of four herbicides used in Vietnam—2,4-dichlorophenoxyacetic acid (Agent Purple, Agent Orange, and Agent White), 2,4,5-trichlorophenoxyacetic acid (Agent Green, Agent Pink, Agent Purple, Agent Orange), cacodylic acid (Agent Blue), and picloram—if “during active military, naval, or air service, they had served in the Republic of Vietnam” unless there was evidence that they had not been exposed. A veteran’s receipt of the Vietnam Service Medal or service in the offshore waters of Vietnam was sufficient to establish a presumption of herbicide exposure. That broad policy was later narrowed so that service on the ground in Vietnam (ground troops) or on its inland waterways (Brown Water Navy) was required to receive a presumption of exposure. Service in the Republic of Vietnam under 38 CFR § 3.307(a)(6)(iii) was defined as actual service in the country, including inland waterways, from January 9, 1962, to May 7, 1975, and service offshore if the conditions of service involved duty or visitation onshore. The VA further stipulated that “mere service on a deep-water naval vessel in waters off shore of the Republic of Vietnam is not qualifying service in Vietnam” (VA, 1997).