In the mid-70s remote tribesmen in South East Asia told stories of a mysterious substance sprayed from the sky or dropped in canisters that caused death and disease in plants and people. They called it ' yellow rain '.
The US State Department suspected it was chemical warfare waged by Communists, but some sceptical scientists believe it is just pollen and that bees and natural toxines are responsible. Who is right?
David Wheeler reports on the evidence in the ' yellow rain ' mystery with people who have spoken to the victims, scientists who have tested samples and those who say it is all a myth. Producer ANNE WINDER