The first large-scale trials of an experimental vaccine against Ebola are due to begin in Liberia.
The potentially preventative medicine was taken under strict security to a secret location in the West African country.
Scientists aim to immunise 30,000 volunteers, including front-line health workers.
More than 8,500 people have died in the Ebola outbreak, the vast majority in Guinea, Liberia and Sierra Leone.
The total number of reported cases is more than 21,000. In Liberia alone, more than 3,600 people have died from the disease.
The trial beginning on Monday will involve injecting a small amount of the Ebola virus into volunteers in order to trick the body into producing an immune response.
But it is not yet clear whether this will really offer protection against the disease.
The BBC’s Mark Doyle in Liberia says that the scientists are well aware of how important it will be to work with the local people if this trial is to work.
Community nurses are being trained in how to monitor volunteers in the months after they have had their injections.
In the meantime, our correspondent says that parts of the largest Ebola treatment centre in the world, on the edge of Monrovia, are being knocked down.
The number of Ebola cases in Liberia have been steadily decreasing. In recent months, there have only been five confirmed cases across the country.