"No tested athlete in a non-corrupt system -- nobody in his right mind -- would have taken that, unless they weren't worried about being tested," Yesalis said.

Yesalis also said that one way to circumvent the testing process is to hire an expert to perform periodic tests to ensure the testosterone to epitestosterone levels stay under the 6-to-1 ratio.

Yesalis said he has been approached four times to perform such work -- including by "a couple of NFL players" -- but declined each time.

Ravens coach Brian Billick commends the league for its drug program. But he has concerns about the over-the-counter supplements that players routinely take.

"The problem that scares me is that the whole [nutritional supplement] industry is so unregulated, and the purity of the substances of what's actually in them [is uncertain]," he said. "Because of the lack of regulation, we ask our players to bring in whatever they want to take [to be approved]. Sometimes it's a combination of things you find in medicines that can present a problem, too."

Although Mitchell played two seasons under Billick and three with the Ravens, the coach said "it would be hard for me to characterize the likelihood" of his steroid use.

It's uncertain whether the steroid issue will send the NFL before a congressional committee, as it did baseball on March 17, but Congress is watching.

"The issue has most definitely attracted the committee's attention, and will be part of our ongoing investigation, since an element of our inquiry moving forward will be to compare and contrast different pro sports leagues experiences with, and responses to, steroid use," said David Marin, deputy staff director and communications director for the House Government Reform Committee.

In the six years since his book came out, Wadler believes much progress has been made.

"We have seen a full-court press on many fronts, seen increased awareness of steroid abuse," he said. "Over a six-year period of time, we have made quantum leaps, including holding baseball's feet to the fire.

"I think every sport needs to have its feet held to the fire. We have to guarantee our kids they are witnessing a level playing field and healthy competition. This is not a problem that is going to go away, as we move into gene doping."

Sun staff writer Jeff Barker contributed to this article.