A team of medical students from Edinburgh university is heading to one of the highest countries in the world to study the effects of altitude on the human body.
La Paz is the highest capital city in the world
It will be the students' second trip to Bolivia in a bid to solve the mystery of mountain illness.
The Apex 2 expedition will conduct experiments at more than 16,000ft to learn more about potentially fatal physiological conditions which can strike randomly at high altitudes.
It is hoped the research, which follows on from the first Apex expedition to the Andes in 2001, could also have an impact on conditions such as asthma and chronic bronchitis which are affected by a shortage of oxygen.
The trip will be one of the world's largest controlled-ascent research expeditions.
We hope to provide strong evidence that antioxidant vitamins could help prevent and treat acute mountain sickness
Roger Thompson, expedition leader
Researchers will investigate conditions such as acute mountain sickness, the potentially fatal high altitude pulmonary oedema and high altitude cerebral oedema.
The students hope their work will increase understanding of human physiology at high altitude and the ways in which people adapt to environmental change.
They will travel to the world's highest permanent altitude laboratory near the capital city, La Paz, and, over a two-month period, help test two new drugs which may provide inexpensive treatments for altitude illnesses.
The team will also work with leading medical experts to test new techniques such as a non-invasive measure of pressure inside the skull.
Expedition leader Roger Thompson said: "It's appropriate that in the 50th anniversary year of the first ascent of Everest, we will seek to answer some of the questions that still surround illnesses at high altitude.
"Apex 2 is a great opportunity to solve some of the mysteries of human physiology at altitude.
"High altitude physiological research is an area of medicine which is often overlooked because of the practical difficulties associated with conducting experiments.
"With such a large number of subjects, we have a unique chance to clarify existing theories of how altitude illnesses develop.
"We hope to provide strong evidence that antioxidant vitamins could help prevent and treat acute mountain sickness."
The medical students, plus three doctors and other student volunteers, who will act as experimental subjects, will leave for Bolivia in August.