The report could open the way to medical care and disability pay for hundreds of reservists who worked on the C-123 planes until 1982 and later developed certain medical conditions.
The Department of Veterans Affairs has denied nearly all their claims for compensation, arguing that any chemical residues in the planes had solidified and therefore were unlikely to pose a threat.
The VA commissioned the Institute of Medicine to review the scientific evidence in hopes of resolving the dispute.
The experts cited studies showing that dioxin — the toxic component of Agent Orange — does not simply remain on surfaces but instead slowly turns into a gas that can attach to dust particles and be redeposited.
"It is semi-volatile, and it will move around the cabin of the plane," said Linda McCauley, dean of the nursing school at Emory University and a member of the committee that produced the report.
Swabs taken from the interiors of some planes between 1979 and 2009 showed levels of dioxin that exceeded international safety guidelines for workers in enclosed settings, according to the report.
The levels would have been at least that high when the reservists were using them.
After the war, the planes were reassigned to reserve units for medical and cargo transport and training exercises. Between 1,500 and 2,100 reservists flew on them over the next decade, until the planes were retired, destroyed or sold overseas.
Records of work schedules have not been found, making it impossible for the experts to estimate the frequency of exposure or who might be at the greatest risk.