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.