The testers from the World Anti-Doping Agency (Wada) arrived unannounced after a Lions training session the day after three Bath players, including England international Michael Lipman, declared they were resigning from the club after failing to submit to a test following allegations at an end of season party in London.
One of the senior members of the Lions part, former England skipper Phil Vickery, told the Daily Mail that he backed fully the testing procedures.
"I fully embrace drug testing. Drug taking has no place in the game and the more we can promote that, the better," Vickery told Peter Jackson of the Daily Mail.
"I've nothing to hide so it's a case of, 'Come and test me as much as you like'. We are ambassadors for the sport and if we want to champion our game, we have to show it's clean.
"If random drug testing stops people taking drugs, then it's to be welcomed. It involves 40 minutes of your time, hardly a huge hassle."