The Ethiopian government has charged 55 opposition members with trying to launch an armed rebellion.
The state-run Ethiopian News Agency reports the defendants were charged this week with "instigating armed violence" against the government following the 1997 national elections.
All of the defendants are said to be associated with the opposition Coalition for Unity and Democracy.
The report says the proceedings have been adjourned until Thursday.
More than 80 other opposition figures are already on trial in Ethiopia, accused of treason and attempting to commit genocide. Those suspects were charged in the wake of unrest that followed the disputed 2005 elections.
The trial has drawn harsh criticism from donors and human rights groups who say the government is trying to stifle dissent.
Some information for this report was provided by AFP.