Campaign groups allege Marcela's real mother was a political prisoner
An Argentine judge has ordered the heirs to a powerful media empire to take DNA tests to establish if they are victims of a forced adoption scheme.
Under the country's former regime, babies were often given to families considered loyal to the military.
Rights groups believe the two children of media mogul Ernestina Herrera de Noble were taken from political prisoners who gave birth in custody.
Felipe and Marcela were adopted by Ms Herrera de Noble in 1976.
They both gave their blood samples at a federal forensics agency, their lawyer said.
They made no comment after giving the sample, but a spokesperson said the family had nothing to hide.
The move to take the sample at the agency rather than the state-run National Bank of Genetic Data - which holds DNA samples of families of the disappeared - has angered campaign groups.
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.
The group's founder, Estela de Carlotto, said on Tuesday that the tests would not be valid and said they would take further legal action to ensure a fully independent investigation.
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.