Campaign groups allege Marcela Noble's mother was a political prisoner
Lawyers for heirs to an Argentine media empire say police raided their homes amid suspicions they were victims of state-organised forced adoption.
The alleged raid took place a day after Felipe and Marcela Noble complied with a court order and gave blood samples.
They were adopted by Clarin media mogul Ernestina Herrera de Noble in 1976.
Campaigners allege that they are the offspring of political prisoners who gave birth while in custody during the country's period of military rule.
They believe the biological parents of the siblings were killed in prisons and their babies were then taken by the state.
Under the country's former regime, babies were often given to families considered loyal to the military.
The Noble family's lawyer, Jorge Anzorreguy, said that both toothbrushes and hairbrushes were seized during the raid at their homes on the outskirts of Buenos Aires.
The raid, he alleges, was carried out under an order of a judge. Argentine officials have refused to confirm or deny that the raid took place.
Felipe and Marcela Noble are heirs of the Clarin media group, considered to be Argentina's most important.
Mr Anzorreguy described 33-year-old Ms Noble as "surprised" at the raid. "Bearing in mind that she voluntarily provided a sample yesterday, she wasn't expecting this," he said.
Groups for the murder victims of Argentina's military era say Tuesday's blood samples are not reliable enough.
They were taken at a federal agency rather than the state-run National Bank of Genetic Data - which holds DNA samples of families of the disappeared.
The Grandmothers of the Plaza de Mayo group, which seeks to find some 500 children born to prisoners or abducted along with their parents during the 1976-1983 dictatorship, has demanded that the DNA be collected at the data bank.
Last month, the Congress backed a proposal from the group, allowing the forced extraction of DNA from adults who may be the children of political prisoners - even when they do not want to know.