BALTIMORE - Late yesterday afternoon, the big horse came off the van. That was Pimlico Race Course's introduction to Rachel Alexandra.

The co-owner of a smaller horse, the Kentucky Derby winner Mine That Bird, had already seen the filly back in Kentucky, galloping every morning before she ran away with the Kentucky Oaks.

"She looks like a train coming down the track," Mark Allen said yesterday.

A filly has not run in the Preakness Stakes since 1999. This one is the 8-5 morning-line favorite.

"Plain brilliant" were the words used yesterday by her new owner, Jess Jackson, who bought Rachel Alexandra four days after she won the Oaks by 201/4 lengths.

Speaking after yesterday's post-position draw, Jackson acknowledged that the colt has not been tested by her own gender. Calvin Borel, who will move over from Mine That Bird, has been her jockey five times and she has won each time, by a combined 43 1/2 lengths. Her connections expect a test from Saturday's 13-horse field.

"We might as well find out and define her," Jackson said.

The owner of Curlin, the 2007 horse of the year, chose his phrase carefully. When it comes to horses, Jackson said he is mainly in the breeding business. "We race to define the horse as a potential breeding partner," he said. He already has announced plans to breed her first to Curlin.

Assistant trainer Scott Blasi said he was pleased to see the filly get the outside post, No. 13. Her presence has sparked some debate about whether entering this race is actually dangerous. There is a lot of talk about whether fillies recover as quickly as colts, since she just raced on May 1, and also whether fillies can withstand the bumps and bruises of Triple Crown races. Four fillies have won the Preakness, but none since Nellie Morse did it in 1924.

"Does our sport need another Eight Belles?" asked Ahmed Zayat, the owner of Pioneerof the Nile, referring to the filly who broke her legs galloping out after last year's Derby and was euthanized on the track. "We all know what happened to Ruffian," who was fatally injured in a match race with Derby winner Foolish Pleasure.

"I did not want to have that part of it on my watch," Zayat said.

That quote, offered as a rationale for why Zayat had considered entering a second horse to keep the filly out, offers one clue as to why Rachel Alexandra's former owners did not point her toward the Kentucky Derby. They saw the oncoming media tornado and passed. Then they sold her for a reported $7 million to $10 million, dependent on incentives.

Hall of Fame trainer D. Wayne Lukas, who has two horses in the Preakness, said that when it comes to fillies racing against the boys, Rachel Alexandra makes the cut.

"Believe me, if I had Rachel Alexandra, she'd have been in the Derby," said Lukas, who trained Winning Colors, the last filly to win the Derby, in 1988. "Are you kidding me? That would have been a no-brainer. I'd have led her over there and said, 'Boys, just get in the gate. You're in deep crap.' "

Lukas elaborated on why he thought the filly is a good fit: that she has dominated her races and she has a running style that keeps her forwardly placed in the race, which should keep the bumping and grinding to a minimum. He added that she has a pedigree for the distance and that the field does not appear to include any superstars.

"I don't think she'll get intimated," Lukas said. "She's not some little violet prancing around. . . . She's got all the equipment to get the job done."

None of the other trainers ached to take on the filly. David Fawkes, trainer of Big Drama, said he may have avoided the Preakness if he had known Rachel Alexandra was coming. But Fawkes also said, "Not taking anything away from her - when she runs, it seems like a lot of people duck her. I don't know if she's caught the best horses yet."

Without the filly, all the attention would be on 50-1 Kentucky Derby winner Mine That Bird, who prevailed at Churchill by 63/4 lengths. A main plot line here is that Borel, who rode Mine That Bird in the Derby, switches to Rachel Alexandra. Borel has committed to riding her for the rest of the year.

She will be the first Preakness favorite who did not run in the Kentucky Derby since Linkage in 1982. Whimsical, in 1906, is the only filly to go off as the favorite and win. Three fillies lost as the Preakness favorite - Fruit Cake in 1917 (fourth), Genuine Risk in 1930 (second) and Winning Colors in 1988 (third). Rachel Alexandra also is the first filly since Fair Star in 1927 to run in the Oaks and the Preakness. She is the first filly ever to run in the Preakness after winning the Oaks.

The top four finishers in the Derby are all entered along with Derby favorite Friesan Fire, the Delaware Park-based colt, who is 6-1 in the morning line, the same as Mine That Bird.

Without the filly, a lot more attention would be paid to the questionable future of horse racing in Maryland, after the Magna Entertainment Corp., owner of Pimlico Race Course, declared bankruptcy in March. As potential buyers line up, it remains unclear how the Preakness will be treated as an asset. The state of Maryland filed motions contending that it has the right to match any offers made on the Preakness.

Pimlico's oddsmaker made this much clear: This race is a referendum on the filly.

"This isn't about male or female," Jackson said. "It's really about the best athletes, male or female, who have durability and speed, and can go two turns [around a racetrack] and not break down."