German investigators want to retest a mystery saliva sample found in the holiday apartment from where Madeleine McCann went missing.
Portuguese forensic tests on the sample apparently found no DNA match to the new suspect, German drifter Christian B.
But the German authorities believe their scientists should carry out their own tests because the sample - thought to have been found on Madeleine's bed - is potentially vital evidence and they hope they can match it to their suspect.
But the Portuguese police (PJ) are unlikely to send the sample, partly because of recent criticism by the German prosecutor Hans Christian Wolters.
He said last week the PJ still believed that Madeleine's parents were responsible for their daughter's disappearance from the apartment in Praia da Luz in 2007. The PJ ruled them out as suspects in 2008.
It is understood the German authorities would apply the same forensic techniques as the Portuguese.
There may also be legal restrictions that would not allow the sample to be sent abroad for retesting in such circumstances.
In 2012, Scotland Yard detectives visited a Portuguese forensic laboratory when they were about to launch their own investigation and their request to retest hairs found in the apartment was turned down.