Takar's team experimented on the crew to obtain medical data to help combat disease on their world. These experiments proved to be harmful to the crew as they suffered torturous pain and the medical experiments were risky.
When discovered, Takar threatened to destroy Voyager unless they allowed the experiments to continue. As a result, Captain Kathryn Janeway threatened to destroy Voyager with the Srivani still aboard, forcing the Srivani to leave the ship. (VOY: "Scientific Method")