The inquiry was set up three weeks ago to investigate whether the Socialist government had been responsible for the so-called Anti-terrorist Liberation Groups (GAL) - death squads. But the Socialists were able to muster the votes of the Catalan and Basque nationalists to reject plans to call the former defence minister, Narcis Serra, and the former interior minister, Jose Barrionuevo.
The Catalan nationalist party had earlier said it would support the questioning of the two former ministers. Their defection drew the teeth of the 32-strong inquiry, which yesterday threw in the towel and decided to dissolve itself.
The collapse of the commission is an embarrassing setback for the conservative opposition Popular Party, which had called it into being.
The Supreme Court, which is conducting its own investigation into the GAL scandal, is pondering whether to call Mr Gonzalez in connection with covert anti-terrorist operations during the early years of his premiership. The court is due to question Mr Barrionuevo after parliament voted last week to lift his immunity as an MP. Mr Barrionuevo will be called on suspicion of kidnapping, misuse of public funds and association with an armed band.
There has been much talk in the Socialist camp recently about the undesirability of having "parallel" inquiries.
A number of judges warned that the parliamentary inquiry could clash with the juridical one, thus casting a shadow over the credibility of the Senate commission.