Given the background of the clubs - Barca representing the Catalans and Real the Castilian seat of a once repressive government - the passions aroused are more akin to England v Scotland in their intensity. Much of Spain grinds to a halt and even weddings are rescheduled to avoid the competition.
Into the Nou Camp - with its 112,000 all-seated capacity - tonight comes the Real coach, Jupp Heynckes, who will know that it is 14 years since the club last won a league match there. Yet the Dutchman must triumph or else Barca - with a game in hand - will take a potentially-decisive five-point lead at the top of the table.
While Heynckes is chewing his nails on the bench, the hottest reception in a cacophony of noise will be for Christian Karembeu, the French midfielder who turned down Barca in favour of their eternal rivals after a bitter 18-month tug of war.
The 27-year-old Karembeu struggled initially, but struck form in Real's 1-1 draw at Bayer Leverkusen in the European Cup quarter-finals on Wednesday. The result, which leaves the six-times European champions with a foot in the semi-finals for the first time since 1989, also proved that Savio Bortolini, the Brazilian who joined Real in December, is finding his feet.
With Savio on the left of midfield and Karembeu down the right, Heynckes may finally have hit on the winning formula which could save his job. Meanwhile, his Barca counterpart, Louis van Gaal, found his own best team almost by accident.
A combination of injuries and international duty forced a change in tactics and the effect was instantaneous. Since then Barca have started to look like a team rather than just the sum total of exceptional individuals like Rivaldo and Luis Figo.
"This game comes at a good time for the team," Van Gaal said. "The are in good shape and what is more important they believe it and feel it. The players have great confidence."
However, if Van Gaal may be quietly thankful for the batch of injuries that contributed to reshaping the Barca line-up, he may now be thinking that there can be too much of a good thing. He will have only one natural, central defender, the out of form Dutchman Winston Bogarde, available for today's game. Fernando Couto is suspended and Albert Ferrer and Miguel Angel Nadal, who have fallen from grace, may be recalled.
If they play, then Nadal and Ferrer will have their hands full denying Spanish international colleagues Fernando Hierro and Raul Gonzalez, plus the Brazilian Roberto Carlos.
The player with the most incentive to shine is the Barca utility player Luis Enrique. He will be determined to show Real just how much his game has improved since moving from Madrid two seasons ago. The former defender is now one of the Spanish league's top scorers and a first-choice selection at international level.
"I can't deny that I would love to score," said Enrique, who got to know what it is to be on the receiving end of barracking during five not so happy years at Real. If he does find the net, the noise will be heard in Madrid.Reuse content