McCanns make Oprah appearance - Courtesy Diva TV
Kate and Gerry McCann have recalled the "terror" and "absolute helplessness" they felt upon discovering their three-year-old daughter was missing.
They spoke to US chat show host Oprah Winfrey to mark the second anniversary of Madeleine's disappearance.
Mrs McCann also said she was told not to show emotion when appealing for her return, "because the abductor could get some kind of... kick out of it".
Madeleine vanished from a holiday apartment in Portugal on 3 May 2007.
On Friday, her parents released a new picture of how she might look now, aged nearly six.
The full interview was screened a day after the anniversary of Madeleine's disappearance in the resort of Praia da Luz. Excerpts from the interview were released last week.
Mr McCann described how the couple felt upon realising their daughter was gone.
"I think almost everyone knows that feeling of terror if you're a parent and you've got a child in the supermarket and you momentarily lose them," he said.
"It's something that no parent should have to go through. It's just the most devastating, horrible sensation.
"Fear for your child and your whole existence. Your family existence."
The McCanns - who have two other children - held hands throughout the interview and both wore the yellow and green wristbands that have become a symbol of their campaign.
They were asked about their decision to involve the media in the hunt for Madeleine just a few hours after she disappeared.
"The Portuguese police were saying 'No, no media', but we were desperate at that point," Mr McCann said.
His wife continued: "The feeling was absolute helplessness.
"You're absolutely desperate. I mean, this is our daughter who we love beyond words, and every second is like hours.
"Nothing can happen quick enough."
An image of how Madeleine might look now has been released
In the days after Madeleine's disappearance, Mrs McCann received some criticism for her apparent failure to show emotion publicly.
Asked about this, she told Winfrey she had "spent 72 hours crying" and felt "a little bit numb".
She also said a behavioural expert had given the couple advice on how to behave when speaking to the media.
"They said: 'It's quite important that you don't show any emotion, because the abductor could get some kind of... kick out of it'," she said.
"When you get the feeling that if you do it could be detrimental in some way to your daughter, there's a huge pressure on you to do well."
The full interview will be broadcast in the UK on Tuesday on digital channel Diva TV.