British police want to test for clues 100 hairs recovered from the hotel room Madeleine McCann was staying in when she vanished.
Scotland Yard have identified 117 strands of hair which remain unaccounted for by police in Portugal.
Ninety-eight hairs have no DNA match and 19 more returned only a partial result, from a total found of 432.
It is hoped that advances in forensic technology could hold the key for unlocking clues about Madeleine's disappearance.
But no testing can take place until permission is given to the Metropolitan Police team by the authorities in Portugal.
The chief of the forensic institute in Portugal which analysed the hairs said progress could be made.
Francisco Brizida said: "I can't say for sure new DNA tests that didn't yield a conclusive result in 2007 could now yield an objective result.
"But technology nowadays allows us to go further than years ago in areas like genetic markers."
Madeleine disappeared from apartment six of the Ocean Club in the Algarve resort of Praia da Luz in May, 2007.