It's a mystery fit for the FBI: why two competing Russian television networks have staked primetime success on the same show.

Every Saturday and Sunday night, about 2 million people tune in to RenTV to watch the "X-Files." Then, on Monday night, another 2 million to 3 million tune in to the same show on ORT. And to the executives of the stations, it all makes sense in a particularly Russian way.

"Of course, it shouldn't be that way," said Yulia Yarmarkovicha, spokeswoman for RenTV. "It's not right. But television networks are so new here, and unfortunately, we have to do it this way for the time being."

In the United States, the show, which depicts FBI Agents Mulder and Scully chasing tales of the supernatural and unmasking massive government conspiracies, has been a blockbuster for the Fox television network.

Spawning a movie, a sister series and scads of merchandising, the show attracted a cult following of devoted fans, similar to that accompanying the long-running Star Trek series.

Indeed, it was in part the "X-Files" that solidified Fox's success, becoming the network's signature show. That is the key in a market where a network's success depends on the quality of the entertainment it produces in-house. The idea that Fox would allow another American network to carry the "X-Files" would be unthinkable.

But in Russia, the most popular shows have often been those imported from abroad. Witness, for example, the Santa Barbara craze in the mid-'90s. Thus, a network's success here depends largely on the quality of the programming it can buy.

That was exactly what RenTV executives were thinking when they prepared to launch their channel in January 1997.

"It was important to us to launch the network with a super-strong show," Yarmarkovicha said. "We fought for the right to be the first to show the 'X-Files' in Russia."

With the rights nailed down for seasons one through three, the "X-Files" quickly became RenTV's signature show, as for Fox in the U.S., and by far the most popular both with viewers and advertisers alike. With a Gallup rating of about 4.5 percent, it is still the network's highest rated show.

"Our rating for the show is amazing," Yarmarkovicha said. "And it's the most expensive for advertisers."

On the back of the "X-Files," the network quickly grew from nil in 1997 to more than 70 million viewers across Russia today. Recognizing the show's importance to the network, RenTV quickly negotiated rights to seasons four through six, and is currently in talks for the seventh and final season.

Seeing proof of the show's viability in Russia, and not viewing RenTV and its then 15 million or so viewers as competition, ORT bought the rights to the first six seasons and started broadcasting the show in October 1998, according to Inna Tkachenko, a manager in ORT's film section.

"It's got a very good rating," she said. "The show has the kind of viewership that it will never lose."

And the proof of its loyal viewership is that RenTV's ratings continued to grow even after ORT started showing the "X-Files," Yarmarkovicha said.

It was a bit of a struggle for ORT to get the show going, however.

Initially put in a late Saturday timeslot, it didn't draw the number of viewers the network expected. So, the show was moved to Monday nights, just after the news, traditionally one of the best slots available.

There, the show has gained a 5-7 percent rating on the Gallup system, Tkachenko said.

And executives have been so convinced of its popularity that they picked up all three seasons of its sister show, "Millennium," by "X-Files" creator Chris Carter.

What the future holds is still a mystery. The show ends after seven seasons. RenTV is currently in the middle of season six, and once season seven is over, it will repeat seasons four through seven, just as it did for seasons one through three, Yarmarkovicha said.

ORT is currently wrapping up season five and has not yet decided whether to buy season seven, Tkachenko said. Both channels are looking for new shows to replace them. It remains to be seen whether they'll reach the same conclusion.