Las Vegas -- THE audience has paid to see blood and will not be disappointed.

When the arena plunges into darkness, they rise as one: an 8-year-old in a skullcap that says "Punishment," a tourist in a T-shirt that says "Legalized Brutality," a young woman who is being paid $2,000 to wear a bikini and blow kisses to the catcalls. The bass line of a heavy metal song, its lyrics indecipherable at this volume but clearly delineating some manner of rage, compresses 10,863 chests.

It is time.

Once confined to the underground and assailed as "human cockfighting," the savage sport of mixed martial arts -- a spectacle melding ancient fighting tactics with those of a bar brawl -- is poised to go mainstream. Cage-side seats now sell for as much as $1,000. Fights periodically draw more men ages 18 to 34 than anything else on TV. Peddling raw, real violence to a zealous, cutthroat crowd, the sport has become an economic and cultural force through events like this one, held at the Mandalay Bay Events Center on a Saturday night.

Two men, barefoot and slathered with Vaseline, their hands covered in little more than leather wraps, enter a cage at the center of the arena. For five minutes, they kick and punch and lock limbs, trying to land a headlock known in their trade as a guillotine and designed to cut off the blood flow in the opponent's carotid artery.

At the end of the first round, one fighter -- Kenny "KenFlo" Florian, a former college soccer player from Massachusetts -- rests on a stool.

"Be patient!" his trainer tells him. "God will tell you what to do!"

Less than a minute later, Florian crushes his elbow into the right temple of his opponent, Sean "The Muscle Shark" Sherk, a father of two from Minnesota with no discernible neck. Blood begins to spurt from Sherk's head, pooling on the mat, hanging in coagulating strands from the cage fence.

Dana White, the central figure in the sport and the president of its dominant organization, the Ultimate Fighting Championship, is sitting within spitting distance. Glancing repeatedly at a small monitor to ensure that his TV crew is getting the shot, he begins to chew his gum feverishly.

"Jesus!" he says. "It looks like he cut his arm off!"

The fighters battle for an additional 11 minutes. Sherk wins by decision, but that seems beside the point. Audience members bellow their approval and high-five one other. Later that night, at a news conference, Florian compliments Sherk on the taste of his blood. Outside the room, White runs into Frank Fertitta III, chairman and chief executive of Station Casinos Inc. and another UFC owner. They embrace.

"Great show," Fertitta tells him. "Great show."

Blood is the new black

DO not bother asking whether all of this is OK -- for parents to bring toddlers to the fights, for crowds to scream obscenities at fighters who are unable to knock out their opponents, for thousands of teenagers to mimic the fights in their backyards, then post their videos on the Internet.

It's too late for that. Blood, as the sport's aficionados like to say, is the new black. Mixed martial arts -- also known to less refined fans as "extreme fighting," "cage fighting" and "ultimate fighting" -- "is the sport for these times," said Bas "El Guapo" Rutten.

Rutten is a renowned fighter; mostly retired, he is a trainer and an owner of a Los Angeles gym called Legends Mixed-Martial Arts Training Center.

"There is so much aggression right now. So much anger," he said on a recent afternoon outside the gym, banging his fist against a fence for emphasis. "These days, everybody wants to kick ass."

Today, billboards featuring menacing photos of top fighters -- the most famous people you've never heard of, perhaps -- are fixtures along Sunset Boulevard. At live events, necks crane to see who is in the roped-off sections -- model Cindy Crawford, perhaps, or porn star Jenna Jameson.

The sport will soon become America's newest export, as executives from Southern California and Las Vegas -- the twin epicenters of the sport domestically -- prepare to take more matches into Canada, Mexico and Europe. The perception, right or wrong, that a global market awaits has prompted dozens of fight clubs, gyms billing themselves as mixed martial arts "universities" and upstart fight promoters vying for a slice of the pie to launch operations across the nation.