Italian Di Luca, who had a previous positive for the same banned substance in 2009, failed an out-of-competition test taken on April 29 at his home, five days before the start of this year's Giro.
The 2007 Giro champion has been sacked by his Vini-Fantini team who said in a statement they would be seeking compensation from the rider.
"I'm devastated, I never wanted Di Luca in the team," sports director Luca Scinto said.
"We have built our group on the sacred values of cycling and we made the mistake of complying with a request, expressed many times, by our main sponsor...who asked us to have faith in an athlete who was a dear friend of his.
"Unfortunately this trust has been rewarded with an terrible mistake, which I still cannot comprehend," Scinto added.
Vini-Fantini's main sponsor, Valentino Sciotti said: "He's mad, he's a cretino, he needs treatment.
"What can I say? I believed in the man and in the athlete and it is right that it should be me who takes the blame because I made a mistake.
"I must ask forgiveness from the fans, the team, the other sponsors, my partners and all the other cyclists who are racing in the Giro d' Italia fairly and honestly, and all those young athletes who will be shaken by this news."
Di Luca, 37, had joined the team last month.
He also served a three-month ban in 2007 for his part in the 'oil for drugs' scandal' involving Italian sports doctor Carlo Santuccione.
Di Luca was 26th overall in the Giro standings, 33:33 behind Italian leader Vincenzo Nibali after Thursday's stage 18. The race finishes in Brescia on Sunday.
Nibali said Di Luca's positive test reflected badly on all the riders.
"It's very bad news because it's always all the riders who pay the price of something like this," he told reporters after Friday's stage was cancelled because of heavy overnight snow in northern Italy.
"This kind of thing is never good news for the world of cycling and something we never like to hear."