The World Anti-Doping Agency has asked tennis to investigate Andre Agassi's admission that he took crystal meth in 1997.
WADA director general David Howman would not elaborate on what he wrote in the letter sent to the ATP, but he told The Associated Press he hopes it "would bring a considered response."
"Our task is to protect the clean athletes and to make sure that these sorts of things don't recur," Howman said by telephone. "And if we didn't take any steps, somebody would be knocking on our door saying, 'Well, what are you doing about this?"'
Agassi wrote in his soon-to-be-released autobiography "Open" that he ingested crystal meth and then lied to the governing body of men's tennis to avoid a suspension after failing a doping test.
Howman said the letter was specifically addressed to the ATP, but the International Tennis Federation would be made aware of it.
"The ATP can confirm it has received a letter from WADA," the tour said in a statement e-mailed to the AP yesterday. "When it responds it will do so directly to WADA and not through the media.