The World Health Organization's 194 members on Tuesday choose among three candidates to replace Margaret Chan as global health supremo, with each pledging to reform an agency under scrutiny.
Chan steps down on June 30 after a decade in which new epidemics such as bird flu and Ebola and decades-old campaigns against malaria, AIDS and malnutrition highlighted the complex health burden shouldered by the WHO.
Among the three vying to be the next WHO director-general is Ethiopia's former foreign and health minister, Tedros Adhanom, who if he wins would be the first African to hold the post.
Another former health minister, Sania Nishtar of Pakistan, is also on the list, as is WHO insider David Nabarro, a respected British doctor and diplomat who has spent two decades inside the UN system.
They are bidding to head perhaps the most influential of the United Nations agencies, which is responsible for coordinating the global response to health emergencies and raising awareness of health challenges ranging from pollution to obesity.
Tuesday marks the first time member states will actually get to choose between several finalists.
In the past, the executive committee presented them with a single candidate to accept and applaud.
The process will begin at 2:00 pm (1200 GMT) with each candidate addressing the WHO's main annual assembly in Geneva.
After that, delegates will cast their ballots behind closed doors.
If no candidate is elected outright, which requires at least two-thirds of votes, a simple majority will decide between the two frontrunners.
All three have vowed to push ahead with a broad overhaul of the WHO.
WHO has already initiated a range of reforms since it faced crushing criticism for its slow response to the west Africa Ebola epidemic that killed more than 11,300 people between late 2013 through early 2016.
Chan, a Hong Kong physician who took the reins of the organisation in 2007, acknowledged Monday it had been slow to react to the Ebola disaster.
But she defended her legacy, stressing WHO had "made quick course corrections", brought the outbreak "under control, and gave the world its first Ebola vaccine".
But it is also widely recognised that more reforms are needed to give the WHO agility to cope with emerging threats.
"We live in a changing world, and the WHO must be able to change with it," 52-year-old Tedros said in his vision statement, citing new health perils from globalisation, climate change and unhealthy lifestyles.
The malaria specialist enjoys strong backing from across Africa, but he also faces allegations he downplayed cholera outbreaks in Ethiopia with disastrous consequences -- something he has denied.
Nishtar of Pakistan, the only woman in the running, has meanwhile vowed to "restore trust" in the WHO.
The 53-year-old cardiologist has a good idea of how the organisation works: Since 2014 she has co-chaired the WHO commission on ending childhood obesity.
Nabarro, 67, has spent half of his 40-year career inside the UN system. His combat duties have ranged from malnutrition and cholera to bird flu and the Ebola crisis, which was brought under control on his watch.
Nabarro embraces his insider status, insisting it makes him uniquely qualified to restructure the WHO.
"You really do need to know what the system is like from the inside if you're going to change it," he told AFP last year.