Vietnam is beginning a joint operation with the United States to remove traces of the toxic defoliant Agent Orange.
The Americans used the chemical during the Vietnam war to destroy vegetation cover for Communist forces, spraying 12 million gallons of it between 1961 and 1971.
Vietnamese experts say more than three million people suffered the effects of the herbicide, of whom about 400,000 died.
A ceremony to launch the removal programme was held at the Danang airport, where the defoliant was stored before being sprayed over forests hiding fighters from the Viet Cong, guerrillas backed by the Communist government of North Vietnam.
US-Vietnam ties have blossomed since diplomatic relations were established 16 years ago, the BBC reports, and steps to resolve issues left over from the war have formed a cornerstone of progress.
"I think it's fair to say that dioxin contamination and Agent Orange was one of the single most neuralgic issues in the US-Vietnam relationship," US charge d'affaires Virginia Palmer says.
For years, Hanoi and Washington argued about questions of compensation for victims of the defoliant; but now the US recognises that dioxin, found in Agent Orange, is a highly toxic substance.
Five years ago the US embassy in Vietnam began to shift the focus to cleaning up dioxin hot spots, clearing the path for swift progress on the biggest remaining war-era issue.
