That was the only test failure for the May 25 event at the MGM Grand Garden Arena in Las Vegas, according to an email sent out Friday by Nevada Athletic Commission executive director Keith Kizer.
All 24 fighters on the card, which was headlined by Cain Velasquez's first-round TKO of Antonio Silva, were tested.
Bowles, the 32-year-old former WEC bantamweight champion, was fighting for the first time since Nov. 2011. According to Kizer's email, Bowles' test showed a testosterone-to-epitestosterone level of more than 20-1. The commission's official allowable limit is 6-1. Bowles did not have a therapeutic use exemption from the commission.
The fighter will be temporarily suspended in advance of a future disciplinary hearing in front of the commission.
Bowles lost his fight to Roop via second-round TKO.