International experts gave evidence in the High Court at Wellington about tests performed on the shirt and whether it had been contaminated with evidence from the crime scene.
Lundy has pleaded not guilty to killing his wife Christine, 38, and daughter Amber, 7, in the family's Palmerston North home on August 30, 2000.
The jury was today walked through complicated processes undertaken by staff at the Netherlands Forensic Institute who tested the material.
Institute forensic scientist Laetitia Sijen said she received slides of the matter in March last year, but there was "very little cell material present''.
But after developing four brain markers that the material needed to match, the tests showed the mark on Lundy's sleeve was more probably than not central nervous system (CNS) tissue.
"From the results we infer that human CNS tissue was present.''
The tests were performed in front of an expert from Lundy's defence team.
No CNS tissue was observed on the mark on Lundy's pocket, but that did not mean it was not present, Dr Sijen said.
Defence lawyer David Hislop questioned the institute's error rate and pointed to a newspaper article that showed the institute had 1700 incidents in the past 14 years - which was questioned in the Dutch Parliament.
Dr Sijen said the number of errors compared with the number of tests run was "relatively low''.
Meanwhile, British forensic expert Gillian Leak today stood by her evidence for the defence that the tissue could have made it on to the shirt after travelling from the crime scene.
The Crown has not yet finished calling prosecution witnesses, but Lundy's defence team was allowed to call its first witness early to accommodate Mrs Leak's availability.
Mrs Leak said the officer who handled the polo shirt had come into contact with other police officers who had been at the crime scene, and an officer who had been near Mrs Lundy's brother who found the bodies.
Prosecution lawyer Philip Morgan said Lundy's top had been inside out and kept in a suitcase until September 3, when it was opened by Detective Sean Hansen, who put it in an evidence bag.
"Unless Detective Hansen had brain tissue on him ... then this whole contamination argument is meaningless isn't it,'' he said.
Mrs Leak said the top could have been contaminated by material on a bench where Mr Hansen had taken it to in order to transfer it to an evidence bag.
She also clarified how paint fragments the same colour as Lundy's tools could have ended up in his wife's hair.
Mrs Lundy could have transferred minuscule fragments, picked up in a newly decorated room, by running her hands through her hair.
She also put forward a theory on how a smear of blood came to be on the conservatory window, saying it could have inadvertently come from an officer changing in or out of protective gear near the window.
The trial continues.
- By Rebecca Quilliam of NZME
