Hundreds of people marched in support of animal testing at Oxford University's new £18m biomedical research centre on Saturday.
Students, academic staff and members of the public gathered near the lab site, being built under strict security.
Anti-vivisection activists, who believe animal testing "belongs in the past", want to stop the centre opening.
Supporters of the centre argue it is essential for research into treatments for human medical conditions.
"My message to the extremists is that you will never win"
Physiology professor John Stein said: "Imagine yourself with a drowsy, whimpering three-year-old with meningitis.
"Fifty years ago, that child would have died. Now, due to the discovery and isolation of penicillin in this university, we can stop that child dying."
Local MP Dr Evan Harris told the crowd that he acted as a human guinea pig in tests for HIV and Aids treatments.
He received cheers from the crowd as he said: "My message to the extremists is that you will never win.
"Every single action of harassment, of intimidation or violence undermines any legitimacy your case ever had."
"I actually welcome this rally... it brings questions about animal research out into the open even more"
Laurie Pycroft, the 16-year-old founder of the student movement Pro-Test, which sparked the campaign in favour of the new laboratory, said: "I felt that it was about time to speak out in support of scientific research."
The event was timed to coincide with animal rights group Speak's rival rally at the nearby Cornmarket, which attracted more than 150 people.
At one point, the two rival groups stood just a few hundred metres apart across a "no-go zone" controlled by mounted police.
Voices were raised but there was no direct confrontation.
Thames Valley Police said there had been no arrests.
Mel Broughton, from Speak, which opposes violent protest, told the BBC's Today programme: "I actually welcome this [the Pro-Test rally].
"I think it brings questions about animal research out into the open even more.
"We have to be very clear - whatever Pro-Test may or may not do isn't going to alter what Speak does.
"We have been there for two years and we will be there for as long as it takes."
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