Pakistan have withdrawn fast bowlers Shoaib Akhtar and Mohammad Asif from the Champions Trophy in India after they tested positive for nandrolone.
Shoaib and Asif are Pakistan's first-choice new ball pair
The tests were carried out by the Pakistan Cricket Board three weeks ago and showed positive results for the performance-enhancing steroid.
They are Pakistan's best new-ball bowlers but face bans of up to two years if the second test is confirmed.
Pakistan are due to begin their campaign against Sri Lanka on Tuesday.
"They have tested positive for using nandrolone, which is a performance enhancing anabolic steroid," Saleem Altaf, director of cricket operations of the Pakistan Cricket Board, said.
I have never come across anything like this in my life.... The timing is not great, but if it's going to happen it happens
Pakistan coach Bob Woolmer
"We have asked for a second test (B sample). But for the moment they have been suspended and are being recalled from India.
"Under the ICC anti-doping rules the punishment for a first violation is two years. We don't have our own rules on such matters and might follow the ICC regulations."
The Pakistan team cancelled their scheduled morning training session following the news.
The PCB has named all-rounder Yasir Arafat and spinner Abdul Rehman as replacements.
"I am confident that I shall perform well if given a chance. Indian wickets help spinners and I am hopeful of doing well," Rehman told the BBC.
The International Cricket Council is also conducting random doping tests during the eight-nation Champions Trophy, ranked second only to the World Cup among the sport's limited-overs events.
We (the ICC) take a zero tolerance approach to doping in cricket. We are a signatory to the World Anti Doping Agency code
ICC chief executive Malcolm Speed
But chief executive Malcolm Speed said it would be the PCB who would deal with the matter as they had carried out the testing before the tournament began.
Speed told BBC Five Live: "We (the ICC) take a zero tolerance approach to doping in cricket. We are a signatory to the World Anti Doping Agency code.
"It is very disappointing this has happened, it is very disappointing for these players but we will get to the bottom of it in the next day or so."
Shoaib and Asif have both recently returned to action after spending most of the summer injured.
Shoaib, 31, underwent a double knee operation in February and 23-year-old Asif, who spent the early part of the summer playing county cricket for Leicestershire, has been struggling with an elbow injury.
Drugs in sport have become a huge issue but Speed said cricket did not have a worrying problem with performance-enhancing or recreational drugs.
He added: "Generally cricket has been considered a low-risk sport. The risk for cricket has always been a player who is injured taking a substance inadvisedly to come back quickly from injury."
Australia spinner Shane Warne was banned from cricket for a year in 2003 for testing positive for two separate diuretics, hydrochlorothiazide and amiloride.
The latest incident comes after a torrid six weeks for Pakistan Cricket.
In August, Pakistan forfeited The Oval Test in a row over alleged ball-tampering and this led to captain Inzamam-ul-Haq being banned for four games for bringing the game into disrepute.
Tour manager Zaheer Abbas was relieved of his duties. Inzamam's replacement for the Champions Trophy, Younis Khan, initially refused to lead the side, saying he did not want to be a "dummy" captain.
Former PCB chairman Shaharyar Khan then quit the next day because of his decision and his replacement Nasim Ashraf reinstated Younis as skipper.