SpainVoters in three Spanish Basque provinces go to the polls tomorrow, to elect their first autonomous parliament since the banning of Batasuna, the party widely believed to be the political wing of the terrorist group Eta.
These are also the first Basque elections since the unexpected general election victory of José Luis Rodríguez Zapatero and his Socialist Party (PSOE) over the conservative Partido Popular (PP) last year.
One of the young prime minister's biggest challenges is how to handle the thorny Basque question.
The electorate is deeply divided between Basque nationalists, including a declining but still significant sector which supports Eta, and a large minority of PSOE and PP voters, whose first loyalty is to Madrid.
Tomorrow's elections are also a significant test for the Basque Nationalist Party (PNV). The PNV has dominated the Basque parliament, alone or in coalition, since Spain devolved extensive powers to the region in 1980.
The PNV has always rejected violence, but during the last legislature its leader Juan José Ibarretxe put forward a plan for sovereignty, an ambiguous formula between autonomy and full independence.
The plan was approved by the Basque parliament, but only with the support of Batasuna, which had been allowed to keep its existing seats despite being banned from political activity. Predictably, Ibarretxe's proposal was then massively rejected by the Madrid parliament.
If the PNV gains an overall majority tomorrow, Ibarretxe has promised to call a regional referendum on the sovereignty plan. Mr Zapatero has repeatedly said he will not permit this.
Such a clash would create the worst constitutional crisis since Spain's transition to democracy in the late 1970s.
Until the election campaign began officially two weeks ago, opinion polls suggested that the PNV was well placed to win a slim overall majority.
It was expected that many disenfranchised Batasuna voters would switch to the PNV.
That seems a long time ago now. Despite the fact that, legally speaking, Batasuna does not exist, the group has become the biggest issue in the campaign.
Its strategy has succeeded in setting the PSOE and PP at each other's throats, in a region which saw them united against terrorism at the last Basque elections. And Batasuna's tactics will almost certainly deprive the PNV of an absolute majority.
Batasuna seemed to have played its last card last month, when the Spanish Constitutional Court prohibited a substitute electoral list, allegedly sponsored by the radicals, from taking part in the elections.
Since then, however, a bizarre series of legal and political manoeuvres has left Batasuna supporters with another option to participate, by voting for a hitherto unknown party with the unlikely title of the Communist Party of the Basque Lands (EHAK).
This tiny group of revolutionary Marxist-Leninists was set up three years ago, ostensibly as a split from Batasuna. It had no difficulty in registering as a legal, if utterly insignificant, political party. Last Saturday Batasuna asked its voters to cast their ballots for EHAK, and the whole focus of the election campaign shifted dramatically.
The PP immediately demanded that the government ask the courts to ban this group, too. Mr Zapatero refused, despite some evidence of collusion between EHAK and Batasuna.