Healthy young people who have had Covid-19 are being asked to volunteer for a trial that will deliberately expose them to the pandemic virus.
The experts behind the study, beginning this month, want to see how the immune system copes second time round.
The ultimate aim is to design better treatments and vaccines.
Up to 64 people aged 18-30 will spend 17 days in a quarantine unit at a hospital suite and have numerous tests, including lung scans.
They will be re-exposed to the virus, the original strain from Wuhan, China, in a "safe and controlled environment" while the medical team monitors their health.
The first phase of this study, funded by the Wellcome Trust, will aim to establish the lowest dose of virus that can take hold and start replicating but produce few or no symptoms.
This dose will then be used to infect participants in the second phase of the study, expected to start in the summer.
Volunteers who develop symptoms will be given an antibody treatment to help them fight off the infection.
They will be discharged only when they are no longer contagious.
Chief investigator Prof Helen McShane, from the University of Oxford, said: "Challenge studies tell us things that other studies cannot because, unlike natural infection, they are tightly controlled.
"When we reinfect these participants, we will know exactly how their immune system has reacted to the first Covid infection, exactly when the second infection occurs, and exactly how much virus they got.
"As well as enhancing our basic understanding, this may help us to design tests that can accurately predict whether people are protected."
Prof Lawrence Young, of Warwick University, said: "Human challenge studies have a long history of being able to generate important information about infections under strictly controlled conditions as well as allow the efficacy of vaccination to be accurately assessed.
"They will significantly improve our understanding of the dynamics of virus infection and of the immune response as well as provide valuable information to help with the ongoing design of vaccines and the development of anti-viral therapies."