Former Argentine military ruler General Jorge Rafael Videla has suffered a suspected stroke, according to military sources quoted by the media.
General Videla led a military junta from 1976 to 1981
The 79-year-old general was said to be in a stable condition, in a Buenos Aires hospital.
Gen Videla, who led the country's military junta from 1976 to 1981, has been under house arrest since 1998.
He has been under investigation after accusations of the illegal adoption of children born to political prisoners.
Up to 30,000 people were killed or disappeared in the Argentine military's campaign in the 1970s against what it called left-wing insurgents.
Analysts say attempts to try him for involvement in Operation Condor - a co-ordinated campaign by the Latin American military governments of the era to crack down on their suspected opponents - have so far come to nothing.