"The complete blood bags shouldn't be handed over because they are part of a crime, but yes samples of them could be given and then later the evidence could be destroyed," lawyer Lucia Pedrero told the court on Friday.
The ultimate decision rests solely with judge Julia Santamaria, who has said she will announce her decision after the trial ends on April 2.
The World Anti-Doping Agency has already asked the court to release the more than 200 blood bags found by police raids on an alleged blood-doping ring in 2006. Spain's anti-doping watchdog has said it will do so as well when the trial is over.
Anti-doping authorities hope their analysis could lead to the identification of any cheating athletes, and uncover clues which more advanced tests available today could reveal.
For years, WADA has tried and failed to get Spanish courts to hand over blood bags found in the possession of doctor Eufemiano Fuentes, the alleged mastermind of a complex doping ring that has so far led to the identification of only a handful of cyclists.
Fuentes has said at the trial, which has been running at a Madrid court since Jan. 28, that he treated athletes from other sports.
The fact that Spain's lawyer says there is a way for samples to be given to watchdogs while the evidence remains in police custody could represent a breakthrough in the long-standing deadlock between the two sides.
Since doping in Spain was not illegal in 2006, Fuentes and five other defendants, including his sister and fellow doctor Yolanda Fuentes, are on trial for endangering the health of athletes they performed blood transfusions on with the goal of boosting their performance. Eufemiano Fuentes denies the charges.
Also on trial are Manolo Saiz, former ONCE and Liberty Seguros team sports director, as well as Vicente Belda and Ignacio Labarta, both associated with the former Kelme team.
Pedrero argued on Friday that Fuentes and the other defendants did not follow health regulations by carrying out transfusions under improper conditions.
Fuentes has testified that he sometimes gave transfusions in hotel rooms and kept blood bags cool by transporting them in coolers with chilled soft drinks.
"We are not judging certain sports practices," Pedrero said. "We are judging if they carried out or incited acts that broke regulations on blood transfusions, thereby putting at risk the public health.
"It isn't necessary to show that harm was done, it is enough to prove the mere creation of the risk."
Spain has since passed anti-doping legislation, with its toughest law set to be passed by Parliament in June or July.