Team Klitschko manager Bernd Boente told Bild in Germany that Mariusz Wach failed his post-fight drug test, positive for steroids, after his November 10 loss to Wladimir Klitschko in Hamburg. From Fightnews.com:

The President of the Federation of German Professional Boxing Association (BDB), Thomas Putz has informed us about a positive Sample A," Bönte told the German daily Bild. "That would also explain why Wach has survived all these big hits. Doping is of course is a no-go. It also shows how dangerous doping could be blocking pain."

Uhhhh... buhhh. Well. Look. Steroids don't give you a stronger chin. That's the long and the short of that one.

Anyway, Wach denies taking anything:

"The first time that I heard about it [was when I started getting calls]. I did not take anything. ... I have not received any official communication [that I tested positive]. I'm totally shattered. I look forward to further developments in the case."

Wach (27-1, 15 KO) stood up to a huge assault and some massive punches from Klitschko (59-3, 50 KO), because he's a very tough, very large man. I have no idea whether he took any PEDs or not, but I am confident in saying that if he did, that doesn't explain why Wladimir Klitschko couldn't knock him out.