Psst. Hey, buddy! There's a crack in your Kevlar.

Business-to-business stocks, the bulletproof brethren of mere mortal technology shares, have suddenly started bleeding. After initially holding up as other tech stocks felt the pain from overall economic worries, B2B stocks are starting to fall.

Just look at their leader. The mighty

Ariba

(ARBA)

, which spent most of August and September climbing, suddenly has all the agility of a clipped duck. Since Sept. 22, the stock has fallen more than 30%. Even

PurchasePro.com

(PPRO)

, the little stock that could, can't anymore. Through Friday morning, it's down 20% from its September closing high.

Rough Month
Ariba, like many B2B stocks, is being hit
by concerns about an economic slowdown.

Until recently, a lot of B2B investors were operating under the impression that no matter what happened to the economy, demand for B2B products would continue to surge. After all, B2B software and exchanges are supposed to make the companies that use them more efficient. So in tough times, when companies try to get the most bang possible out of their spending, B2B products have been cast as a must have.

Until now.

"People are starting to question whether corporate America is going to focus on e-business if they're in a slowing economy," says Gavin Mlinar, a B2B analyst at

Sands Brothers

. "Personally, I believe the B2B e-commerce industry is an industry that can persevere through that, but it has affected the stocks."

Who Needs It?

"Clearly, there has been slowdown in demand at various Web consulting firms, which are helping to implement

B2B systems. That's typically a leading indicator," says Patrick Walravens, a B2B analyst at

Lehman Brothers

. "So, sure 80% of

big companies will probably have a

B2B exchange at some point, but maybe they won't all be having it tomorrow."

B2B exchanges are Web sites where companies can do business with each other.

A B2B slowdown over the short term is something that concerns Eric Efron, co-manager of the

(USAUX) - Get Report

USAA Aggressive Growth fund. He counts Ariba,

Commerce One

(CMRC)

,

TheStreet Recommends

FreeMarkets

(FMKT)

and PurchasePro among his holdings.

"There is the possibility that the dot-coms might not be as much of a competitive force," Efron says. "If that's true, then maybe the traditional companies won't feel so pressured to innovate, so they can go at it at a more leisurely pace."

The Dreaded Downgrade

Another sign came out of

Jefferies

earlier this week, when analyst Richard Williams downgraded Commerce One over concerns of slowing sales momentum. In an interview, though, he said slower sales might indicate that the company isn't able to meet demand, rather than that demand is drying up.

But then, a slowing economy hasn't been the only thing weighing on B2Bs. The fact that

The Alliance, the three-headed cult among Ariba,

i2 Technologies

(ITWO)

and

IBM

(IBM) - Get Report

, has been showing signs of weakness lately hasn't helped. Last week, the trio

lost an already announced customer.

Yet with earnings season just around the corner, some see a B2B opportunity in the making with the current selloff. Joe Frohna, manager of the

(FIMPX) - Get Report

Firstar MicroCap Institutional fund, has been adding to his PurchasePro position over the past week. It's already one of his fund's top holdings.

Big Revenue

"Revenue estimates this quarter are in the $13 million to $15 million range. They're going to do more like $20 million," says Frohna, who met with PurchasePro management recently. If the company does hit $20 million in revenue, that would be its second consecutive quarter of 100% plus revenue growth.

Frohna also believes that earnings season will give B2B stocks overall a pop.

"Once they do report their numbers, people are going to say wait a second, these are extraordinary growth rates," Frohna says. "In the face of slowing technology fundamentals, I've got to believe these companies outperform going forward."

But not all B2B watchers are so sure. Ed McCabe, B2B analyst at

Merrill Lynch

, says the current selloff shows what happens to emerging names when more established companies start encountering problems.

"Which ones were bulletproof?" he says. "These stories need a good market to work. In the face of a techscape where valuation has become important, it is very hard to own the more speculative tech companies.

Especially when the more stable ones are being sold by investors."

In other words, watch out for that speeding bullet.