Argentina's Supreme Court has ruled that amnesty laws protecting former military officers are unconstitutional.
Some 30,000 people may have been killed during the Dirty War
The judgement clears the way for prosecutions of officials suspected of human rights abuses during military rule between 1976 and 1983.
President Nestor Kirchner, who called the amnesties "shameful", said the ruling restored faith in the judiciary.
Civil liberties groups say about 30,000 people were killed or went missing under the former dictatorship.
The Supreme Court upheld a decision by the Argentine Congress in August 2003 to scrap the amnesty laws.
The court voted by seven to one, with one abstention, to strike down two amnesty laws which had been in effect since 1986.
The legislation forbade the prosecution of military officers suspected of atrocities in the so-called Dirty War - a campaign waged by Argentina's military rulers against left-wing opponents.
The campaign ended with the country's return to civilian rule in October 1983.
President Kirchner said: "The court's decision has restored our faith in justice. This is a blast of fresh air that signifies the end of impunity."
About 3,000 military officers - about 300 of whom still serve in the armed forces - could be accused, the Associated Press news agency reported.
Ahead of the ruling, Argentine Defence Minister Jose Pampuro said some officers were anxious pending the outcome.
"In a personal capacity, some men who might be involved in some situation are expressing worry," he was quoted by AP as saying.
The Supreme Court ruling came in the case of former police officer Julio Simon, accused in the disappearance of a couple and of having taken their daughter as his own.
Under Argentine law, the decision will act as a precedent in other cases involving the Dirty War.