When you tickle him, he slaps his knee and laughs hysterically.

After rocking himself back up, he asks for more.

Tickle him again, and he falls to the ground, kicks his feet and scoots around on his back.

Then he stands and asks to be tickled again so he can repeat his theatrics.

That's how Fisher-Price describes one of its hottest holiday toys, whose name reflects how hard it is find on store shelves.

T.M.X. Elmo, or "Tickle Me Elmo Extreme," has been selling out at local stores just minutes after it appears on shelves. The toy marks the 10th anniversary of the original Tickle Me Elmo doll.

"We had about 50 of them, and they went within the first 10 minutes," said Marcia Miller, store director of Toys 'R' Us in Janesville.

The story is similar at other local stores, managers said.

Blain's Farm & Fleet isn't expecting another shipment of the extreme Elmos until spring. The store sold out of Elmos after Toyland opened Oct. 21, said Renee Tarnutzer, communications coordinator.

"It's at the manufacture's discretion," she said.

Managers at other stores-such as Target, Wal-Mart and Toys 'R' Us-said they are expecting small shipments but don't know when they will arrive.

The toy retails for $40, but it is available online at sites such as Amazon.com for no less than $130. Other Web sites have developed around the toy, including www.tmxelmotracker.com.

The 15-inch mechanical doll is recommended for children 18 months and older. It uses six AA batteries.

"It really is an Elmo that appeals to all ages, both adults and kids," Tarnutzer said. "I think there's as many grown-ups buying it for themselves as for their kids."

Fisher-Price describes Elmo: "In his most 'x-treme' move ever, he even rolls on his belly and slaps the floor! Your sides will split as you watch Elmo crack up with laughter! And when even Elmo admits he has had too much, just flip the on/off switch."

For the Elmo-obsessed, there's a new Barbie called "Barbie Loves T.M.X. Elmo doll," which is sold separately by Mattel.

Target manager Mary Backenger's best advice for parents is to check regularly with stores because finding an Elmo is partly luck.

"Everyday people are looking for it," she said.

The doll is appealing to younger children because of how it moves, but also because of its marketing campaign, media attention and limited availability, Backenger said.

Only a handful of people saw the toy before its release date.

Elmo comes hidden in a box that looks like a sealed trunk with a tab that says, "Don't lift!" A voice comes from the box that says, "No peeking! Hee hee hee!"

"The marketing was probably very effective," Backenger said.