Underground criminals now have "control of a significant percentage of world sport", according to the head of the World Anti-Doping Agency.
David Howman, addressing a conference in west London, said organised gangs make more money dealing in performance-enhancing drugs than trafficking heroin.
He said their reach extends much further than is widely believed.
Mr Howman explained: "The underworld is involved in betting and in distributing steroids and it's the same jokers doing both.
"The mafia launder the money (from selling performance-enhancing drugs) through the betting industry.
"They might get a return of five bucks for a four buck investment, but they're happy because the money is laundered."
Mr Howman told Sky News he was sure the same criminals distributing illegal substances to the world of sport are also involved in match-fixing and spot-fixing.
He said: "I don't just think it, I know it, and this is not going to improve unless someone does something about it. If you can get away with it, you will continue."
He added: "I have been saying this for years but now Interpol are justifying it. They have the numbers and information, and they're really worried about it."
Mr Howman is attending a two-day conference at Twickenham Stadium dealing with the problem of tackling doping in sport.
During his keynote speech, he also controversially stated that the British Olympic Association (BOA) rule on banning doped athletes from the Olympics should be tested in court.
Under BOA selection rules, any athlete who is found guilty of doping is banned from ever representing Team GB at the Olympic Games.
But he said this could represent a 'double jeopardy', whereby the athlete was punished twice for the same offence.
He said the rule "could be construed as an additional sanction to the world-wide two year ban from sport".
It was a shame, he said, that when the sprinter Dwain Chambers tried to challenge his lifetime ban in the High Court, it was dropped before reaching a full hearing.
"That hasn't been decided by a court of law and it would be useful if it were."
http://news.sky.com/skynews/Home/World- ... 3612?f=rssI'd like to see some sort of proof really, but I can't say I'm shocked at what he's alleging....